Massey-Ferguson has unfortunately really gone downhill since the '80s when the company had a bunch of financial problems. They changed ownership more than once before AGCO bought them and AGCO has been pretty poor with parts for older tractors. You would do fine with, say, a MF 135 where the aftermarket makes a bunch of parts, but if you get one of the lower-volume models like your 451, you are out of luck. I found that one out firsthand in the past too.
Deere has extensive parts availability, although they have less availability for parts on some of the third-party stuff they rebranded like the Yanmar-made compacts they had in the '80s through the 2000s. They have good availability on anything they themselves made. CaseIH and New Holland have pretty decent availability on parts for implements, and the little we've needed tractor parts for relatively newer units, they've had them.
You have a bunch of choices in a ~45 PTO HP open station utility tractor- Deere 5055E, the CaseIH Farmall 50A/NH Workmaster 50, Kubota M5660 or
M6060, just to name a few from the big players. I have a Deere 5075E (same tractor as the 5055E but with different engine tuning) and it's a nice, solid, maneuverable machine I would not hesitate to recommend. I mainly picked it over the CNH twins because the Deere dealer chain actually had tractors and wanted to sell them, and Kubota only makes the
M7060 with options I didn't need and didn't want to pay for.
Massey-Ferguson's compacts started out with the Toyoshas for the first (10xx) series of compacts they made. They were all three-cylinder machines. The Isekis came after that for the 11xx through the 16xx series, and they make the current 18xx series, but didn't Shibaura make the 17xx series?