In the UK all the FB's (which was not very many) and some FD's had them. Two small girls can fit, or one average person if he sits sideways with feet on the other side. You just take the storage compartments out and they bolt right in. You have to cut an opening in the rear plastic trim piece for the top latches to fit through. There is already an outline where you cut. You also need longer side trim pieces, shorter back carpet, and covers for the seatbelt rolls. There are actually a fair number of FB's with rear seats in the US. I think it is easier to sit back there than in a BMW 840/850 rear seat.

I read somewhere on another RX7 site I believe,that all Aus/NZ models came 2+2 and it was an option in Japan but the North American market FBs never had it available. But then,what's the point of back 'seats' in a 1st gen? The back seats in my 87 Celica are bad enough.

haha we turned rotaryxsevn's fb into a 4 seater, weve been stripping the interior and took out the behind the seat compartments and it has 2 perfect buckets and its pretty comfortable if youre short haha less weight and 2 new seats cant beat that with a stick