Depends what cam you're after, if you just want fast road you could probably get away without putting cut outs in the piston and you probably would use standard valve springs, if you want sporty cams you will need valve springs aswell and the head machined to get the correct spring heights (probably about 200 quid for that) i recommend Kent Cams, they've done wonders for us, Del is a genius. You'd probably have Vernier Pulleys on it aswell to dial the cam timing in perfectly. Lightening a flywheel, just take it to an engineering shop, that's what we do, the clutch sits in a stepped bit on the flywheel, that must be kept there you can't just machine the whole lot flat. It depends on how much you take off it doesn't need to be balanced after although it is better too.