Noticed in my search that most transmission swap questions are 'fitting a 13B to a 12A transmission and power related and such.
I have a 12A/4speed in a Homebuilt car and a very noisy tranny (they aren't filled with ball bearings, are they?) and am looking for a 5 speed that will fit (very limited space and the 12A one is already in there)
I'm finding 13b transmissions listed but no (?) 12a ones...
Will a 13b unit fit without a outside size difference?

 

That transmissions are indeed all ball bearing. But at this point, they are fairly worn out.

Having only ever seen one 4 speed 12A transmission, I can't say if the 5 speed is any larger. Probably slightly longer. However all transmissions are interchangeable. You can use a 13B transmission from a GSL-SE up to a '92 NA. The turbo R-type transmissions are much larger, though also much stronger.

You need to match the flywheel, clutch assembly, starter and slave cylinder to the transmissoin and you may require a custom driveshaft.

Any pictures of the car?

Edit..Oh, and I almos forgot. The shifter location changes based on the transmission. In 84/85 it moves farther back. Tail housings swap and shift rods can be modified.

 

....thank you...as I mentioned, the space is very, very tight...not worried about length, but width is at a premium....

 

...couple more