hi mate , i know these engines respond well to having tubular exhaust manifolds fitted , freeflow exhaust system air filters and chips my mate got about 30 bhp by fitting the manifolds only.
make the tubular manifolds yourself , get the bends and laser cut flanges (send him a manifold gasket) from lance at ojz engineering in lincoln i would say they would cost you about £100 a side to make and get welded.
then if your hungry for more power fit throttle bodies these aint cheap at a £1000 (merlin motorsport in burton on trent built loads of f1 engines etc ) and pectel management at £1300 for the ecu and wiring harness and £450 for live mapping you should see a solid n/a 300bhp engine like the one they use in the ford supervan 3 and have you heard that its fookin amazing and goes like shit of a shovel
but a good cheap starting point is the above then move up to the next stage if you want
hope this helps
cheers paul