It would be virtually impossible to update a "B" without it being obvious.

126-250cc. Standard frames, Standard fairing, Standard ignition, no airboxes. Any brakes. Cut off dates 1st January 1985 - 31st December 1991

A "B" frame,fairing and ignition(2x boxes) are unique from the rest of the v-twin range and airboxes would be easily seen.

Sure an "A" has lapped faster than a "B" anyway, MR Lougher in '90!