if i have an aftermarket skunk2 manifold on a b16a head with a stock TB (i think) What would i have to do to fit say a 74mm Throttle body? Or anything 68-74mm? Im a noob so just need to know before i pick one up.

 

Go read up on the effects it will have. Both the intake and throttle body. You'll have to basically port match the intake manifold to the same diameter as the TB. You'll need an air powered rotary tool and burrs to remove the aluminum.