The 5 speed is the ZF5, but don't bother if this will never leave the farm, the main advantages are less fuel consumption on the highway and less engine noise, longer engine life when used on the highway, but hard to find and expensive, t18/t19 are almost worth scrap cost.
I don't see why it wouldn't bolt up, I have a spare diesel transmission so I could measure the hole centers if needed.
another options is dual transmissions, low could be in the range of 16-20 to 1
or deeper, even better than the rear end, although with a single transmission the deep rear gears are great.
The front loader means you bonked your head, and we will all be expecting to see pictures by tax day