That brings back memories! In 1971 I had a '63 Triumph TR6 that wheelied really well.......I made a 45mi. run to the city and parked at the pub, threw down the sidestand
and stepped off, the bike flipped over behind me as the 'unrestrained' fork tubes rose in the lower legs. Seems the previous owner of the front end I had put on had not tightened
the bolts enough in the bottom that held the tubes back. Really good that I hadnt been inclined to show off a wheelie that day!
Later that year a friend with a BSA Rocket Three did have his separate during a wheelie; he almost flipped back when the weight of the wheel and lower forks came off, but held
it then leaned to the left and spilled it into the median that fortunately was there. Next day he had it back together and riding; new unbent fork tubes of course.......
Hadnt thought about this stuff in a long time..........watch those wheeelies!