I feel pretty good at 73, but I remember being young. Not that guy anymore by any stretch of the imagination.
I cycle every other day for an hour on a bicycle on a trainer. 24.5 mph average currently. Would translate to slower on the street. I won't ride on the street anymore around here though. That feeling of being invincible has left the building.
I'll defer to the track day and wealthier men on installing an 8-valve head on an old Norton engine. As much fun as it would be doing the retrofit and saying I did it, I think it is impractical for a P11 750. Mine is already on the ragged edge of being able to stay together. One should never say never though.