On a side note, why don't you see many if any mokes in rallies?

mokes have a definite advantage - a good driver can do really well in a moke, a great driver is unbeatable

weight can be more like 150kg different (homologated weight of a moke is apparently 450kg), they're also a longer wheel base which gives them more stability. They do have a lower centre of gravity by virtue of no roof and 5 less windows worth of glass

12" or 13" wheels make some difference, and with big tyres you can get more speed out of first gear, but Kelvin who won this year is using 12" wheels with A539's which will fit on a mini.

I think they usually use mini diff ratios, a 4.1 or 4.2 diff doesn't give you enough speed without a gear change.

Mokes are also all in the same engine capacity class, so there are no competitive mokes with anything less than a 1275

but maybe if i had a twin cam bike head on an a series motor.... who knows

More power isn't always a good thing in Motorkhanas. It becomes way too easy to overdrive and hit the corners with way too much speed. That said, having it is a good thing, using it is the important part. When I first started out, I found having less power helped me drive better, and I still overdrove and probably am still doing so some now. So a bike head, is probably a bit OTT for this type of sport.