Can anyone tell me what to look for spec wise when looking for a T4 for a Cossie?

For example you see them on Ebay with T04 Comp housing A/R.50
T4 Comp wheel.
T3. 48 exhaust housing.

What does "trim" mean too, seen a few saying "this trim, that trim"

Any help would be appreciated.

The car its going on is running greys(for now), RS500 Cooler, L8, 6.7:1 Comp, and revs to 8250RPM. Will shortly be getting Siemens injectors, GoTech management and head work.

He is aiming for high 400bhp figures, maybe even 500 mark, in it and is adamant a T4 is going to be used.

Any help from you lot would be greatly appreciated.

Cheers peoples.