I can see all the points mentioned so far - I have a 135 ... and a MF40 with FEL. The '40 is an industrial - a real machine - very capable, 2WD but heavy, with a strong front axle and 7.50-16" tyres, power-assisted steering, and with a real 72" loader, 50 years old, but designed to keep working ... and she still does, really well. The 135 is a legendary agricultural-spec tractor great for the work it was designed for, to which a FEL can be fitted ... however ... it is overall a lighter machine, the 6.00-16 front tyres and 3-piece front axle's load-carrying capacity is limited, lack of power steering is also a valid point. That said, a FEL of a sensible capacity on that tractor, complemented with a rear counterweight, operated in a sensible manner and within its limits would make it a very cost-effective machine for a hobby farm or acreage residence. It would just take a bit longer to do what the '40 will, but the ground compaction aspect (especially in damp soil) would be much less of a concern. Ensure the components which will be facing higher loads (front axle and tyres, steering box, linkages, joints etc) are well serviced, maintained and lubricated. The steering boxes on these tractors are getting really worn nowadays, but they're very easy to overhaul and reset clearances and preloads. Ensure it actually HAS oil in it! A lot have had it all leak out - won't last long then! A product called "Liquid Grease" from I think Castrol, or an equivalent, is a much better option ... it won't leak out!
Go for it, I say!