I have 79 RX-7 GS which I bought new. I blew the transmission last summer, missed 3rd gear at the Epping Dragway in NH. I also have 1980 engine & drive train which has about 100K miles on it. I took it out of the '80 last year.

My gear-head Mustang neighbor says put the 1980 engine in my '79. What I really want to do is rebuild the tranny for my 79, and put the '80 engine in something else, doesn't have to be an RX-7.

Any thoughts?

 

The 80 trans will fit right into the 79. However, later trans are different.
If the 79 trans is not rebuilable, use the 80 trans. I wouldn't swap the engine, unless there was a valid reason.
You can always locate another trans to fit the engine, if you intend to install it in something totally different. Any non-turbo trans will bolt up to the 80 engine.