Your comments about the Aoshima first generation RX-7 are absolutely correct - the body is shaped nicely for some of the first gen racers, but the interior is very shallow to accommodate the battery pack since the kit was motorized. I've yet to get my hands on the Fujimi version, but like you, I think it is the same. As for the Tamiya kit, it is 1/24, and was released as both a Series I (SA, molded in green) and Series III (FB, molded in white) first Generation RX-7. The SA version included "waffle" wheels, like the Monogram kit and the FB included the bizarre rotor shaped wheels that were a Japanese market only item. The SA & FB nomenclature refers to the beginning two digits of the VIN's. Both of the Tamiya releases are as scarce as hen's teeth now. I have both of the Tamiya kits and have compared them to the Monogram kit - the wheel wells line up exactly. The Monogram kit builds into a series II first generation RX-7, US spec, with left hand drive and a beautiful little rotary engine. I'm happy to see this kit come out again. Of course, I'm a bit biased.
The page for RX-7 kit information ... right here Erix's page is full of great information about these and other RX-7 kits.