the 79-80 rx7 tranny has the shortest length to the shifter.
The Miata transmission is just as long ( I know, but it is, I've measured both and I have the rx parts here to compare.
THe later model rx7 (second gen 86-91) has the shifter exeternally mounted back kinda like the Getrag situation. I've looked at mine, and with minimal work, (no more than the getrag), the shifter can be relocated 6 inches further forward.
Now, Martin Reimer's rotary GT just has the engine almost as far forward as the front crossmember, and his 12a first gen setup with the 81-85 tranny fits the stock location just fine.
Someone correct me if I'm wrong, i've only seen the photos and talked to Marty for a very short period of time.
Also, the 12a's are much easier to mount given thier stock setup of mounts, but we all want power from the slightly larger 13b's
I know that the early covers will fit late model 13b's, I just have to see about the crank angle sensor for the ecu, or you can just use an early style dist. with one of the aftermarket carb adapters that are out there to throw away the FI.
In most cases I would never tell anyone to go carb over FI, but the RX7 FI was not every sorted out until 1990 which is known as the s5 version. It still was not as maintence free as non rotary cars, but it was as good as it got until they went 13btre (twin turbo).
So, I have the stuff here and all the measurements have been made for test fits, and I believe I will be droping in a 1990 13b non turbo with an 85 tranny into my opel sometime before October. I just have the sell of my house and the purchase of another taking precendence. Oh, and the arrival of a 74 manta that might get bumped ahead.