white smoke and loud clanking when put into drive-- 97 sl2 automatic

Well I know you're right about the coolant leaking into the cylinders from the white smoke, but the only scary thing is how hot did the engine actually get? If the engine heats up too much it is possible to crack a cylinder wall and have an internal leak (the cylinders have little jackets or "vavles" that run by them which allows the coolant to absorb the heat from the cylinders). If the interal leak is really that bad and you have a cracked block, then all you can really do is a) buy a new engine and pay a butt ton for labor or b) buy another car around the same amount as it would cost to put a new engine in. And yes the coolant definitely screws with your oil, but it does more than just thin out the oil, it contaminates the oil so the whole time you have that particular oil circulating through your car you're just letting the contaminants cause corrosion on anything it touches. :( As for the car hangin' at 2k rpm and then dropping is just the engine trying to circulate the oil. My saturn only revs up to 1500 rpm when first started, so this may be related to the contaminants in the oil. (This may also be related to the transmissoin acting up) The clanking noise is probably the transmission. I'm pretty sure that the synchronizers in the transmission are worn out which makes it hard for the tranny to match speed with one gear to the next one (or in this case hard for it to smoothly match gear speed with the idler gear to the drive gear). This may just be a sign that's saying tha the transmission might quit on ya sometime. The rough riding can be a number of things. I had the same problem with my Saturn, and me and instructor were working on it and the car computer said that it was just the cam sensor sending inaccurate readings to the computer. That was a simple fix of just clearing the code. I hope your problem with rough riding is just as easy man. Now for the A/C; I'm sure you're right on that diagnosis. The coolant that finds its way into the cylinders is probably why the car is losing coolant. You should have those bearings replaced sometime soon or sometime before you start using the A/C heavily. Those bearing were put there for a reason, and that's to keep things from rubbing against each other and wearing metal away. So definitely replace those before using the A/C heavily. (note: A/C stands for air conditioning which means it's not limited to just absorbing heat from inside the car and then spewing it outside. In some cases the heater will actually work more efficiently if the A/C module is on.) That's what I can figure out from the description. I hope you can fix this man. Good luck!

Engine is cheaper to replace at this point,the loud clanging is the engine compressing coolant and has most likley done extensive internal damage.

This is from 2009. Congratulations on a useless necro.