Ah don't bash the 3100 Its just as reliable as your 3800'*. And don't discard that Cutlass just yet.
As with any engine, its all in how they're taken care of. I've got one with over 200,000 on the clock and it runs amazingly perfect. Got another with 96,000 on it and no problems. But with your 3.4, I dispise those engines (as do most mechanics). I had a Cutlass Supreme with the 3.4. It was dead by 80,000 with the same low end knock that you're experiencing. And there are ways to temporarily hide it.. as it sounds like the previous owner did. The 3400 and 3.4 are quite different. The 3400 is a decent engine.
The 3.4 was pushed out rather quickly in 1991 to compete with the Taurus SHO. Because of the hurried rush behind it, it was never really refined as it should have been. It HAD the potential to be a powerful, reliable DOHC engine.
Either way, I wouldn't stick any money into that engine. What are you looking to get for the car as-is? The rest of it seems to be in excellent shape. Perfect candidate for a L67 swap .. or parts.

Post it over at w-body.com/forum or I can do it for ya if you'd like. The guys aren't fans of those red interiors, but it doesn't hurt to post I'd just hate to see something in such good shape end up in a yard.

Im sorry to hear about your car but I look it up and the shop time for removal, installation and transfer of parts is 13.4 hours.

I surely don't mean it in a bad way. Everything has its own problems and its own solutions. Just talking in general, the 3100 seems to be put down as being problematic and a waste of money. And its usually because of the common problems they have that aren't fixed ahead of time, leading the 'average' consumer to preach to everyone that its the spawn of the devil.There isn't anything special about 'em.. they just do what they're supposed to do. Same goes with the 3.4. That engine has its religious followers. The only experience I've had with the 3.4 is bad.. which doesn't make it a BAD engine. It has its share of problems like everything else. Preventative maintainence usually avoids the huge expenses that the 3.4 seems to commonly have. As far as why my 3.4 died, I had no clue. I bought it with 50,000 on it and it was religiously maintained, as it was my first car, and ya all know how you love your first car. It was a beautiful car, but by the end, I was more than happy to see it hit the dirt. I just don't want anyone to get the wrong impression.. no offense is meant in any of my posts.

As far as that Cutlass, is that the '97/Convertible spoiler/lip I see on the rear? That'll go on eBay for sure, if you're scrapping the unit.

I have 50,400 miles on my 3100...Don, should I just go ahead and change the intake gaskets now? How much should I expect to shell out? Is there any other type of preventitve maintenance I should have done to be safe? Thanks

So far so good with my engine. Drives great (and sounds great with the intake). It was taken care of, at least in terms of how it was driven. I'm sure it had the oil changed regularly, but I noticed some gritty crud when I took the oil cap off and put my finger in the front valve cover. I really hope I don't have serious problems with this engine down the road. I hope to keep this car for good. I'm pretty happy with it so far.

I agree, a lot has to do with the maintenance. Honastly, the 3800 in my Bonneville has cost me more in repairs the the 3.4 in my Grand Prix has. Mostly its because I do maintenance religiously on both, but I had the Grand Prix since it had 30k miles, so its been well taken care of. My dad had my Bonneville for the first 70k of its life, and didnt take great care of the motor. It never had problems for a long time, but around 75k the upper intake went, along with a lot of coolant and oil leaks. My friend used to run a shop, and he'* told me horror stories of otherwise good motors that have gone to hell early because the owner only changed the oil twice in 60k miles.

It can be an issue with used cars unfortunitly

Ok...well I may do it now...as long as it won't cost a lot. I got my coolant system flushed right after I got it, and they never COMPLETELY filled the coolant, and I HAVE noticed I have less coolant than I did a couple weeks ago.... :o

Either engine should swap in fairly inexpensively. They're such a common engine in yards, anyone can pick one up for next to nothing. Heck.. I've seen people trying to GIVE them away with no luck. I'd just pull the complete engine/PCM/wiring from the donor car. That'll be the most headache-free way of doing so. I'm not an expert on the 3.4 by any means, as I dislike the thing, but its quite different from the 3100, so its safe to say that next to none of the sensors or wiring is gonna match up. Thats why I'd just pull the complete unit from the donor car. I guess if one were to do that type of swap, the 3400 would be a slight advantage over the 3100.

On the other subject..
Keep your coolant in check like mentioned. Keep it clean and keep it fresh. It turns basically acidic once it starts to break down, which will tear away at your gaskets. People so often let it get that far. Once it turns acidic and starts eating away (which is yet unbeknown to the owner) they have the cooling system flushed. Voila! Thats the final straw.. coolant and oil mix.. and the engine sludges up. Because of the mileage this usually occurs at and the high expense to have a shop make repairs, most of these cars end up in the yard.

Phoned around today, the motor rebuilt was quoted around 5000, installation on it is about 20-30 hours, which i do belive is correct. I had the Saturn Dealership look at it, the guy said sounds like a connecting rod on the crank, bearing is gone. My dad is pressuring me to sell it to the parts yard, the offerd me 1000 for it.

If you wanna ditch it, post it on the w-body.com forum and see if you can get anything there.

Coming from my little corner of the world, I believe that the 3100 and 3400 have earned their bad rap from people that simply don't maintain and/or check fluid levels. They're not as rock solid as other engines (GM, Ford, and DCX). But, customers have come to expect the same out of domestic manufacturer'* engines compared to what the foreign auto market sells (Honda, Nissan, Toyota, etc.). By in large (and are still failure prone, but not as prematurely), those foreign engines can go a very long time between maintenance intervals without a catostrophic failure. GM and other domestic OEMs brag about their extended services intervals (100K mile tune ups, DexCool, etc.), however the engines just aren't capable of going that long; unlike thier foreign-name branded counterparts. Unfortunately the 3100 and 3400 require a little more care than what the 3800, Ford 3.8, Chevy 350, etc. require and that'* how they've developed the bad reputation. And that also is the reason why used 3100 and 3400 wrecker engines are so expensive -> high demand because of premature failures! No supply, but high demand!!