As a kid, back when we had flogged out SL70s and Z50s and the occasional KD80, a mate's dad rebuilt a CR80 for another friend. Of course, everyone had a go...
It was funny, really - all the adults came back talking about how they couldn't keep the front wheel on the ground - this was because they had to plant their arse on the back of the seat, and totally ruin the weight distribution.
One of the other kids and myself were the right size for it, and had no such problems...
That said, I recall watching Pete Marmont riding a young Jay's KX60. On tar, with Pete sitting on the seat-tank junction, it would both lift the front wheel and spin the rear. I haven't laid eyes on Pete in narly 20 years, but he was not a small man at the time.