The main use of the tractor would be for field work, plowing, discing, cultivating and its been brought to my attention that the T/A on the 656 might not be the best for that application but fine for running the haybine and baler. Now I need to consider if I want more HP to do the field work.
I was fairly certain that's a good part of why IH created the TA, to help with tillage when things got tough, you could grab the chicken stick and pull through it. Some of them (maybe most) with the 1-way dog design don't appreciate being used as a low gear, like when you're going across a field and just want to use the engine braking to slow down, I've heard some folks say don't just pull the torque. if it's pulling and you need more hp, fine, but if it's in a freewheel condition, not so good.
I've never really been around a 674, more than just walk past one at a sale, but my grandpa had a 656RC & a 756RC and I have a 756. Comparing a 656 in RC trim vs a 674, you'll have a much taller tractor with the 656, but if you've found a 656 utility, they should be pretty similar. I wouldn't be afraid of either.
Depends alot on the ground for what you can pull. Our soils in Northern MO will make my 756 smoke some pulling 3 bottoms, and will work 140 hp pretty good if you try to pull 4-16 or 4-18 and try to make good time. Typically, I've seen guidance for plows to be 1pto hp/ inch of plow width, with a range of 12-25hp/bottom depending on actual size of plow, plow brand make, tractor
ballast, soil type, condition and groundcover. 10-12' disc and field cultivators would probably be well within either of these tractors' capabilities.
