I am familiar with the 51 but I believe that the drums come off separate from the hubs. When you get to 1 1/2 Ton, things change. The screws definitely have to come out first then you can work on getting the drum off. If you can turn the drum then you shouldn't have too much difficulty. You need to strike the flat face which is against the hub and this tends to break the rust bond. Using heat usually results in a squealing drum when it is reinstalled. turning the drum while you are pulling it off is sometimes helpful.
My front ones were tricky to get off because of a ridge that developed inside the drum. Therefore I attached a chain to two of the studs, and with the outer wheel bearing removed, I yanked on the chain with an iron bar. That worked quite nicely.
