We did this last year on 300 2-T's.
Actually we booked a Lesotho Roof training long-weekend for that weekend on the 300's, only to find out closer to the time that the Retro Roof is the same date, so we decided 'what the heck let's do this event while we are in Lesotho', and then the rest of the remaining days we will continue with the technical riding.
It was a lot of fun, old bikes, and new, not really a race but more an event, although the front runners, as in any event, gunned it to the end.
Dally, from Pongola Dirt Zone organiser of the annual Pongola 500, who is extremely capable on bikes to put it mildly, did it with a 1290 with his young laaitie as pillion, 790 can easily do it yes...