My advice is to be careful jumping to conclusions. While this is a killer truck and I'd love to have it in my driveway, there doesn't seem to be a way to be sure when the four wheel drive conversion was done on this truck. So, perhaps it was done in 1935, but it could have been done at a later time.
I think the four wheel drive conversion was influenced mainly by the buildup to WW2. I think MH and other manufacturers were trying to convince the government to purchase their equipment. I read somewhere that MH converted one 1935 Model 51 truck to FWD late in the model year and then converted more in 1936. I would have been easy in 1936 or 1937 to convert a 1935 truck to MH FWD. Cunningham did the same thing with their Caterpillar rear drive unit (think half-track) for both the US government and the Canadian government. The key would be to have paperwork linking this truck serial number to a MH conversion order. I know I'm being picky, and I want to believe that this truck is a true 1935 era conversion, but for now I just remain envious. Perhaps the conversion was done during WW2 when new trucks were just not very easy to obtain?
Anyway, it's a great truck and I hope to learn more about it.