Ive never seen a victa with 8&*
Theres 6&8 which was common years back
And then with the later alloy bases from the mid 90's they had 7&8.
Its not the wheels its the bearings.
They are crap. Sure they are a ball bearing but they run in plastic races.
Im pretty sure that the rover & masport bearings run the same centre bore size. Thats what i would swap to if you do a great heap of mowing and dont have a big cupboard full of spare wheels.
I would go back to the rubber wheels with no bearing and keep them oiled, they will last more than a lifetime.
Might look a bit like arse.