Can you interchange parts for Fordson Super Major?

Unfortunately, the answer is Yes and No. As for internal engine parts, one must be careful about the interchange of parts between the FMD and FSM.
Same for hydraulics. However, much of the tinwork, running gear, transmission, electrics etc are fully interchangeable. As far as the reference to the 5000, one must realize there was a Fordson 5000 Super Major and a Ford 5000...few parts are interchangeable with the Ford 5000.

Your first step should be to identify your engines as Mark I, II, III, or IV series, copy down your engine serial numbers side by side and then when you read and re-read your I&T manual in
the diesel engine section, make detailed notes or
highlight the paragraphs in the manual that discuss FMD FPM FSM similarities or differences.
I believe Intertec refers to differences mostly by
before and after a specified serial number. An original service manual will refer to parts interchangeability by both Mark series and engine
serial number... drop by every old Ford/New Holland and New Holland dealership you ever drive by and ask if they have a an original Fordson service manual packed away in the back or boxed up
and stashed in the attic. You may come across one. If the service manager has been in the business for 40 years or so,,, their face will generally light up, if not; you generally get blank stares, shrugs and mutterings of "Is this guy out of his mind?" I stumbled across a dealership in Iowa while passing through one time and the close to retiring service manager literally broke down when I came in inquiring about information dealing with Fordson tractors. We maintained a close friendship for several years and intermittantly I received in the mail
a page or two or three of old service bulletins he
came across. I think before he retired and hence
passed on he went through every old box, file, and
stack of papers in that entire dealership to find
and send each and every morsel of Fordson information he could find.

Mark I engines: to serial number 1425096
Mark II engines: from 142096 to 1591023
Mark III engines: from 1591023 and up

*These numbers are as accurate as I have been able to research and discern from Fordson records.

I am the unfortunate owner of a 1963 or 1964 Super Major Diesel. What's unfortunate is that the PTO shaft was rammed through the front PTO gearbox housing, thus fracturing the small round cover(on the front of the PTO gearbox housing), and creating hairline cracks in the threads of the 2 lower small front cover holes. I was able to interchange the hollow shaft off a Major diesel, but the Major Diesel PTO gearbox housing is smaller (DON"T ASK ME HOW I KNOW.....PLEASE!!!!!) Anyway, if anyone is aware of where I can obtain a PTO housing with or without internals, I would be grateful. The rest of the tractor is in excellent running and operating condition. Casting number is EIADB, or EIADD, or EIDBB. Then, 7252B IFI.

Thank you!!

Sincerely,

John