Manifolds and crossovers on "different engines'? Do you mean the 5.3L?

That'* right there is a 5.3L W body available. The only item to note though on a dipstick tube area is that the L26 with NU3, Cali emissions uses a different dipstick than the rest of the 3.8L'* and the 5.3L motor. However all W body dipsticks 97+ will work w/o any issues. I checked Compnine.com and all the tubes are the same except that Cali version. And I have installed headers on the Cali cars before w/o any problems.

listen to bill. get the correct dipstick. it fits fine and works. don't be like me and try to bend it. it'* way too different to consider. when you swap them you can also get a new rubber dipstick grommet at advance auto for like 2 or 3 bucks. says only fits RWD apps but that'* false. it fits us too --- dipstick swaps first, then install headers.

the rear header will go in from the bottom without issues. it'* painless after that.

Oh it MUST be from a 3800 powered car. as long as it'* a 97+ 3800 you're good to go.

The GM part number is the same for the dipstick tube in the L36/L26/L67/L32 and LS4 with one exception. The L26 with NU3 (cali emissions) has a different part number. I verified headers fit that tube with an install on a couple of cali L26'*.

my bad bill. remember my local yard sucks and is retarded. i specified 3800 only and they still messed it up the first time. it helps for JY that are not pick & pull sometimes to specify exactly what you need and adding that it must be a 97+ GP, Impala, or Monte w/3800 can make it easier for them

Thanks guys for all the help, it is much appreciated.

I visited the nearest pick and pull and got a W body tub & dipstick for a whopping $2.31. I even got lucky in that the donor Grand Prix already had the heads taken off making access much easier; that bolt is pretty well hidden if you don't know what you're looking for.

When I got the tube off, no rubber seal came with it. From underneath, I could put my finger in that hole but didn't feel a rubber seal of any sort. It was hotter than blazes out so I gave up. Will I need this seal, or does one exist on my car that I can reuse?

Also, with the Speed Daddy headers, will I have to drive my car open downpipe until I can get things welded up? Or is there something I can do to connect the stock exhaust to the headers (speed daddy) temporarily to get me to an exhaust shop? I'm assuming I need an exhaust shop to do some of this regardless, as I'm purchasing a 3" high-flow cat for the car as well.

You can reuse your seal. I might be wrong, but I think those bolt right up to the stock exhaust.

Anyone know what the part number is the for the Magnaflow hi-flow cat I'll need? It'* 3" inlet / outlet, correct?

i have a 03 bonneville sle and these will bolt right up with lil modifications correct?

Yes. 2000+ is all the same.