parts needed for restoration 20 valve turbo

Is a supersprint system inc cat best for 280 bhp road car.
Where can i purchase an uprated alloy radiator and uprated alternator. Should I change exhaust manifold and downpipe when dropping engine and subframe for resto?
The car is 1998 20valve turbo never been restored and 42000 miles.
I have an uprated turbo and chip from flea.

Supersprint system should be okay, but you need to be aware that this is mild steel and will rust. A better solution would be to get a custom exhaust made.

An alloy radiator for that power, it isn't necessary. Same as uprated alternator. Why do you need that? Several coupes with 400+ BHP all run the same standard alternator. If it's dying, then get it replaced.

Does the exhaust manifold need doing? Would be worth checking if it is cracked and it will be a far easier job to replace with the engine out of the car if it is cracked.