We've got to be careful here branding figures around, most of the UK people are using one dyno (Steve's).

On his dyno;
a stock wirespliced mc18 running on 95ron unleaded will make about 62bhp
a very well put togeather mc21 running on 97ron unleaded made 67bhp
a stock '91 RS250 nf5 running on 100LL avgas made 72bhp
a pretty much perfect late (PGM-II) F3 mc21 running 97ron unleaded made 74bhp

All those peaks will be over 11000rpm, the RS and F3 will be nearer 12000rpm.

Basically no 250 is going to make 73bhp at 10800 rpm on that dyno.

To make 70+bhp on an NSR bottom end you need a lot of things to be very right indeed.
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Please do not PM me technical questions, if you can't find it on the Forum start a thread