Like Nick, I'm not an expert. The minitwins rules are listed here (though some clubs interpret things differently)
http://www.minitwins.co.uk/
Broadly
- The engine is to be left largely alone (72HP limit, no capacity increase)
- The rear shock can be replaced, fork internals can be replaced. Original forks and wheels must be retained.
- Original brake calipers & master cylinder must be used
Supertwins:
Seem to allow more engine work, full brake caliper & fork swaps (gsxr front ends etc), wheels can be swapped.
Jambo