There's another issue I have from my first outing on my track bike ... After a while my front brakes would completely lock up ... the bite in the brake lever gradually got less & less until the whole lot locked up.
I have just rebuilt my master cylinder but that doesn't mean it's right ! but I am also using cbr600 calipers with RO converters...both calipers seem to lock up ... If I whip out the 8mm spanner release the pressure in either ...I can get on my way again !
Does anyone know if this is related to using the VFR master or just inept brake maintainance! Should I be using the CBR 600 master ...

I will go with inept brake maintenance. There is a relief hole in the master cylinder to let fluid escape back into the resevior. Your brakes are locking up because the piston in the m/c isn't returning all the way and/or there is debris in the relief hole. As your brakes heat up, the brake fluid expands If the fluid can't go into the resevior, it pushes back on the caliper pistons. This escalates the heat build up and makes the fluid expand more. This cascading effect continues until the brakes lock and shit gets expensive.

Take apart the m/c and make sure this hole is clear. (Sometimes the brake lever is the culprit, not allowing the piston to return so check that too.)

The problem is at the m/c for sure.