55 bhp is pretty easy/cheap with a MC28 using race pipes and an MC21 flywheel. Failing that you could grind out the washers in the standard pipes and just get the flywheel. It shouldnt cost more that £30 for a MC21 flywheel...if you can find one. Any more than that and you will need a HRC card which only used to cost £70, unfortunalty you cant buy them so have to find a complete PGM with card which usually cost nearer £400.

In my opinion 60bhp is pretty easy from 21 with the wire splice and airbox mod. 70bhp will also be a lot more work and cost a lot more than an hours work.