Rob, dont start chasing numbers mate!

personally 400hp is a weird number to go for, your caught between a t34 and a t38.

you can get your's to a nice 340-350hp with the injectors and turbo you have so the cost to go for 30/50 more hp isnt really worth it in my opinion

if you were to do it however you'd need a t34.63/ t38 , a set of Siemens/ Greys and a new chip to suit.

assuming you buy used parts

£120 -£150 injectors.
£250 - £325 for a decent chip
£300 - £400 for a turbo.

personally i'd stick with what you have, it will make for a quick road car, you're only running 18 psi at the mo, you can easily run 28psi through it and still keep the same injectors and chip.

what chip do you run?

Matt