Heh heh, sorry I found this amusing.
Im a Nissan guy and im in between projects. I was looking at getting a miata and therefore lurking around to scope out the community. I just had to respond to this post, as I feel I can set a few things strait.
The T25 off of the 300zxTT and the s13 (91-98) SR20det's are identical. A T25 is a T25, right? Now, im more if an inline motor guy and i hate all things "V", but im pretty sure the left and right turbos from the 300zx's are the same; the right side turbo is mounted 180deg, if that makes and sense.
All Nissans (past 91) and thier turbos respectivly use a standard flange. T3 or T4 I believe. Im not sure what, say the Greddy turbo kit would use, but front what Ive read in the last few minutes on this forum it sounds like Mitsubishi-type IHI turbos. I honestly dont know anything about them (i stay away from Mitsu's), but i do know if aftermarket turbo manifold manufactures copy Greddy, then no, yould need to have a T3 flange welded on. It's realy not too big a task though.
I wouldnt bother with a T25 though. If your going to go through all the trouble of building a turbo kit for a nissan turbo, then look into the later ball bearing turbos found on the S14/S15 Silvia SR20dets or the GTi-R (RNN14) Pulsar SR20det turbos. They are dual ball-bearing and are the basic turbo upgrade for us SR guys. A stock motor with an S15 turbo is capable of over 325hp without too much trouble. A bit much for a Miata, but you get the idea
A T25 (which is non-ball bearing) tops out at about 250 on an SR. Once again, im not certain of what that means to a 1.6/1.8 Roadster engine, but its a good reference.