I found a rather interesting turbo that a fellow member has for sale, and I think it came off a diesel engine, and it is about the size of a T88 (or something around there), so would that turbo even work on my car.

And as a second question about a TO4 or 60-1 turbo, what kind of supporting mods do I need to put a turbo like that on?

 

Single involves new fuel system from pump to secondary rail. Larger injectors, etc. Some even advise for a larger ignition system.
The Diesel Engine turbo, if I remember correctly has a smaller exhaust wheel and larger compressor wheel.
Fine for a low reving diesel motor, but not a good setup for a high rev rotary.
good luck though.
I have a listing on my website of all the costs I've come across going to single if your interested.

 

My car is already single, I have a TII.

Shouldn't the stock injectors support 375 HP (or something around that neighborhood). I'm really not shooting for anything over that.

And the diesel turbo that I am looking to play with, is about 3-4 times the size of the stock S4 TII turbo. Rather than spooling to soon and then clogging the exhaust, I think it would never spool. But I am wondering if anyone has ever put a turbo like that on there RX-7 with any success.