If all 6 plugs are out, yes, you should be able to turn the engine in either direction with minimal effort.
Now we need to see what is causing the hold up. Remove the serpentine belt and see what happens. If no change, disconnect the torque converter from the flywheel via the 3 bolts.

Sounds to me like a spun bearing. Happened on my '94 the day I bought it, and drove it home! It only got home on a flatbed...
A few months and a junkyard motor later, she was up and running... and still is.

That'* my guess from here, FWIW.

By all means go through the individual checkpoints to rule out other possibly locked bearings, transaxle etc. When my bonnie blew, it was a somewhat slow process, and I was able to start it, even after it was flat-bedded home, but it would only run a short while before making noise and smoke and bogging down. So, your scenario is decidedly different. I'm hoping you have a better result too!

Wondering if I am having this leaking manifold problem? 94 Buick Le Sabre 90,000 milesI am having a problem for some time with the SE Light coming on. Also there seems to be a very small leak somewhere in the cooling system with an ounce or two missing after 2000-5000 mile. I found one small leak at the thermostat gasket and the leak rate dropped way back but there still seems to be something else. Since the car is a 94 Buick Le Sabre 3800 finding the correct scanner is a very big problem for me. The last time we had it on a scanner was at 85,185 miles. Codes P0118,0171,0131 and 0342 were detected. The Mass Air Flow sensor was cleaned a bad connection to the temp sensor was repaired. The technician thought that there may be an issue with the Power Control Module or its connector if the light came on again which it did. The car did run much better after this but issues with the SE light are still with the car as well as the minor coolant leak. Car is still getting around 28-32 Mpg on the highway at 70 mph indicated with AC on and windows up.

Jim K. 1994 Buick Le Sabre 3800

Did you find out what was wrong? If you are suspecting major engine damage I would remove the valve covers and see if everything looks o.k. when you turn the engine over by hand. If everything looks o.k. I would pull the oil pan and see if you find a problem there. I think you can remove the oil pan without taking anything else apart on that model. If that looks o.k. you will have to pull the heads to see inside. If that'* the case you would probably be better off finding a good used engine. I see them on ebay for as little as $300-400. Its a lot of work but it is doable.

I do feel a bit stupid for not finding out sooner, my air conditioner compressor froze up. Thanks mike for telling me about the fan belt. I wish it had been the first thing I looked at. I have never had a belt grip so tight that it kept the motor from turning. I wish I could run it w/o the air right now but I don't know what belt might work, if any. Thank all of you for your help.

Glad to here its not major engine damage! I wonder if you cam replace the clutch without removing the entire compressor? I just had my compressor replaced because it would not hold Freon. With a filter, dryer, Freon and labor it was $650. Its 90 degrees here today, worth every penny!

I believe there is no way to short belt it, you MUST have a pulley down there. They make a bypass/delete pulley, you can try replacing the clutch only, or just replace the compressor and be done with, as you did.

Nothing beats basking in A/C

Other cars I have owned were able to run without the AC compressor working. Usually the clutch would allow operation with a seized AC compressor. It may be that that djhplm was unaware the AC was on. Once I had a problem with an AC compressor that was "solved" by simply turning the AC off.

manual or automatic.... could be a bad TORQUE Converter forced in lockup if that is possible, or the cooland in the cylinders rusted the rings , if the coolant got in the oil bad main bearings.

I have seen it happen plenty of times where the compressor seizes, the clutch burns up and won't disengage anymore. Only way to get the pulley to turn again is to get a new clutch on there, and never plug it in.