slim jim transmission

I have a 1963 pontiac grand prix with a 421, which needs a new transmission. The trans in it now is not original, but I'm trying to replace it with one that is. I believe the original automatic that would have been in the car was a slim jim. Does anyone know if the same slim jim transmission was used with the 421 as well as the 389? Thanks Rob

Hope this helps.
http://www.rodandcustommagazine.com/techarticles/82698/index9.html

Hey, along this line I have a project question. I am restoring a 1965 GTO with the stock 389 Tri-power. I have the 2 speed Powerglide but would really like to install a 4 speed automatic, possibly with overdrive. Is there a trans that will bolt or use an available adapter or can you modify a TH400/350 BOP by adding a 4th overdrive? Thanks, Jim

Hey, along this line I have a project question. I am restoring a 1965 GTO with the stock 389 Tri-power. I have the 2 speed Powerglide but would really like to install a 4 speed automatic, possibly with overdrive. Is there a trans that will bolt or use an available adapter or can you modify a TH400/350 BOP by adding a 4th overdrive? Thanks, Jim

Welcome to AF

I think your best bet is to use a BOP TH400 with a Gear Vendors overdrive bolted to the tailstock. OD can be used in all 3 gears. Sometimes first OD can launch you better than first gear on its own.

You could use a built - up THM200 R4, so long as you get the multi-bolt pattern housing. Don't try a stock one, you will tear it up.

A built-up post -'87 TH 700 R4 would work, so long as you can get an adaptor. Advance Adapters might have one.

BTW you will get a better response in future for starting a new thread on a new subject, instead of tacking it on to an old thread.