There are things you can do without breaking the bank completly. Make sure you have a decent ignition system. Don't know what Caterham fitted but I have got Lumenition. Yes, see if there is a better camshaft available (don't know what Caterham fitted). Is it suitable for unleaded, don't know what Caterham did (mine is not a Caterham engine) if not you may want to consider getting the exhaust valve seats converted. Get it set up properly on a rolling road Even that lot will not be that cheap Finally regarding the axle I suppose that depends how you intend to drive it. Round the track hopping curbs it may not survive but normal fast road driving may be OK I have a Ford axle but I understand it was the Ital axle that permitted Caterham to make the long cockpit. If you have one of those I do not know if a Ford axle is possible