!!!Big transmission problem!!!

About a month ago almost all my gears were grinding. Most peope told me it was my sycro or low fluid. I finally took it to the shop and they said it was my clutch it wasn't engaging. I just bought a clutch and took the old one out. Found out that the spring on the disc poped out. So I put in the new clutch and thought I was all good. Drove it around pop it into third and it grind and poped right out. I figure my third is gone, since it wouldn't go in. Every other gear are driving fine. Any body know if a b18a third gear would fit onto a b18b1 trans. Because I have a b18a trans laying around. If it won't work does any body know where I can get a DECENT price on a trans
Thanks

One more thing I put a stage 3 clutch in and a 7.5 lb lighten flywheel. When I drove the car it seem like the factory clutch pulled way better. Is it because my trans getting weak or what? It seem slow now.