The MF20D used different sheet metal than the 20C and 40B. Sims built the factory cab for the 40B. It is a ROPS / FOPS cab. However the same cab with minor modifications was used for the 20C, 30B, 40B, and 50C. I have not seen a 20D with a cab on this side of the Atlantic. You will most likely have to do some modifying to get it to fit.
If you post some photos of the cab, I should be able to tell if it is a Sim's. The Sims cabs bolt to the loader uprights. My 20C has the Sims cab on it. The Cab attaches in two points, the loader uprights and the axle. you will most likely have to fab new axle mounts as they were different depending on what tractor the cab was mounted to. You will also need to create some sort of adapter from the loader to the cab mount.
I think the most challenging part will be the cab floor. You will probably have to do considerable fab work on it.
Please post photos of the two and I can ID the cab.