forget to say, u can use a standard 3sge clutch plate, but the plate/disc has a smaller diameter. u will lose about 8mm of clamping.(thats how much smaller the disc is).This will still work but obviously not good.
I thought i could buy a gt4 clutch plate because the disc would match properly, but the spline is wrong. what u need to do is get a clutch that has the centre part(spline) off a 3sge, matched with the disc of a gt4/mr2. that what i did. got it from daikin and i got it cheap for $400.
hope this helped keep us updated on your conversion.