No Mazda uses KKK's I believe, they have octogonal exhaust inlets in the turbine housing side... it's weird. BUT... since this is a 1G Miata with some kind of (presumably) aftermarket manifold, it's probably a standard T2-style flange.
He'd do best with a T25G rather than just a T25. Yes, there is a difference. If you're looking in the Nissan world of things, the T25 came on the CA18DET, and the T25G came on the first and second generation SR20DET's. It also came on Z32 but I am not certain it uses a standard T2-style flange.
I actually have a T25G but of course I refuse to part with it because it was rebuilt and the center section is rock solid good.