Power train differences
 

If i did switch from a 12a to 13BT would there be other things i'd have to change out like the rear-end or anything else?

The 13Bwill bolt up to your 12A tranny, so no worries there.

I ran a steet (4) ported 13B with a Racing Beat Holley intake and complete exhaust using my original '79 drivetrane aand had no problems.

Isn't the 3rd gen engine the 13BT-REW?

Not sure of all the differences, but from what I understand, it is slightly different than the 2nd gen 13BT.

I dunno, maybe I have no idea what I'm talking about here.