Personal opinion here

Pull the motor apart now and check the bearings for signs of detonation
Chances are you have already lunched the pistons and rings anyway

When your happy with the bottom end put it back together

If its got stock pistons in it now your as decompressed as I'd want to go without making it doughy off boost

With all those crazy injectors on it maybe you should make one of them pump a methanol/water mix to help cooling intake temps and providing more bang for your buck

Then get it tuned to suit

Thats what I would do if it was me and you weren't looking to spend huge on reinjecting it and building it for boost

As for the clutch and box...I'd use the T50 but its not going to handle abuse much more than the stock box
And if you use the clutches Dellow says to use they use the standard A pressure plate so its no bigger or better than what you have
Unless you get the flywheel redrilled for a Toyota 200mm clutch like mine is
And if you lighten the flywheel it will rev faster.... might take your ankles off if you take too much off it though



And Skylines do break... often... and they cost more to fix