"Newer" could still be in the 1960's compared to that MF 50. Several books and sites list the 50 @ 38 HP. They're actually rated @ 32. (I've had a couple 50's and an F-40, which is the same tractor) An "upgrade" to a 135 or 150 Massey would be a big improvement. They are 38 PTO HP, and have many more features that put them in the "modern era". The 50 was to the 35 what the 150 was to the 135. Slightly heavier, a little longer wheel base, bigger fuel tank, bigger radiator, better power steering, heavier front axle with more clearance, and in the case of the 135 vs. 150, better air filter system. The "100 series" Masseys are, imho, the best small tractors ever built. They still hold their own against newer tractors. If you can find a diesel, you'll get the best small diesel engine ever to grace a tractor with the Perkins 153-3.
Further on, the 245 and later 250 are logical replacements for the 50/150. They soldiered on with that same Perkins diesel. (A variant of that very same engine is STILL used today on the 431)
I bought a NEW 150 Massey in 1973. (1972 model year tractor) I still have it. I keep a detailed service and repair log. In 33 years, I still haven't filled the note book. These are simple, basic tractors that any "amature mechanic" can keep running. No electronics, No plastic parts, just lots of time-tested easy to work on components.