The 731 is as good of an engine as any, the only down side I can think of is if it does need repair as all engines will need at some point, it may not be as economical to rebuild. But to say that it is a weak link is incorrect. We had an 8550 and currently still have a 4w305 and they were and are both good tractors. The weakest link on the 8550 would be the universal joints, I dont recall how many hrs you could run until replacement was neccessary but it did seem to be the weak link of the tractor. The 305's articulation was redesigned and we still have never put a u-joint in it. Good transmissions, heavy differentials, and a large engine, these tractors were a beast in their days. I am thinking it has a 12mm injector pump which if you wanted some serious power, all it would take is a little tweaking.