OK- I'm just about to put a TII fuel pump into my 90 GXL....
It's from an 87 TII.
I was under the impression that the S4 and S5 fuel pumps were the same, but after reading a bit of scott89t2's page (1300cc.com) It now seems that the mounting brackets ("fuel pump holder") are different or something??
I really hope not.. and this is the first I've heard of it...

 

The fuel pumps are different...the s4's have s 16 gallon tank and the s5s have a 19 gallon tank, so obviously the pump frame must reach farther down for a s5...putting in an s4 will yeild you only 3/4 of a tank of useable gas

Id say you could take the pump itself off the s4 frame and install it onto your s5 frame and be ok, but I havent ever done it.

 

Yes they 87 model pump has a shorter bracket than the 90 model. You can just swap the pumps and it will be OK.

 

OK- so the actual motor unit, wiring, and attachmnents are all the same, I just have to use the bracket that is in my tank now, and just swap the 87 pump on to it...
Correct?
I hope so..
Is is just a direct fit in onto the bracket? I don't see why Mazda would change little things like that....

 

The little pump is the same. You can swap pumps between all 2nd gen RX-7s, and FDs. Of course, flow is different. See attached pic of FD pump installed in my '86 NA frame.