[mickmate]

I agree with pretty much all above, original cars used a big in small out version of the TL. In decent shape they are a great tranny for these cars. If you're getting a used one look over the gears in the gears that get ripped through, pretty much the first 3. Since you're using an IRS you can use any length trans but you may need to shim mounts for driveshaft angle not to be too severe. Once that's set up the diff isn't moving so you're good.
Think about clutch type and set it up accordingly for your use. You don't want an on/off switch or a chatterer. Big clutch in a small car you can pretty much go stock.
Do a little research on throw out bearings. There are plenty of people that dislike the hydraulic internals and they'll tell you why. I like serviceable and adjustable external but it can be pretty close to our frame rails.