Again, unfortunately MTD's trannies are not compatible with any other manufacturer's.
It's not like it will break fast, but working it hard (such as heavy pulling) will cause it to die within a season or 2. I'd just make sure the next 'work' tractor you get has a tough rear. The older Craftsmans have a Dana-Spicer rear end that is pretty good for that type work if you're looking on the cheap side.
If you want one that will last forever, look for an old International Harvester-Cub Cadet or John Deere garden tractor with the 3 speed or 4 speed manuals. However these machines still hold their value extremely well, so you'd be lucky to get a running JD 210/212/214/216 for less than $750.
The 3 speeds will hold up fine to the pulling. If you get heavier then look at one of the 4 spd. units in the 200 series JD's and early 70's model Cub Cadets both of which have a granny low 1st.
F-250 XL RC/LB 4x2 Power Stroke Diesel
2010 John Deere
Z710A 48" cut
1999 John Deere
1985 John Deere
212 w/38" deck
1983 John Deere
420 w/54" hydraulic front blade
1974 John Deere
140, 54" hydraulic blade, 3pt. hitch, tandem disc, plow, 48" deck
1971 John Deere
112, 38" deck, all original, down for engine rebuild.
1967 IH Cub Cadet
124 w/creeper box, disc, plow
1947 Economy/Power King
Tractor S/N 590, fully restored.
Certified John Deere