Green, it seems low, but that was the min power requirement. Yes, a larger tractor could be used, but the 4430 was period to the 6601, and it sure handled it fine. I don't know the 4430's exact PTO Hp, but was guessing around 45-55. I know it's not monstrous.
A 4430 was around 125, and the 4440 was around 131. They could put out lot more depends if the farmer tweaked with the fuel pump and injectors. There is a 4430 running around my house putting out almost 150HP.
I agree either one of those would pull it well. I have saw a pic of a 150HP 4630 pulling a 7721 combine before.
GS, the Hp quotes I gave, were min PTO Hp required to run the 6601, NOT the actual Hp of the 4420 to 4440 tractrs. I just confirmed that any of these can handle the 6601 just fine. The brochures showed a 4430 pulling one, too.
The numbers you told was more like on the #30 combines. Even the #96 required a good 60+.
Even the SP versions had more than just 50HP to run. Like you stated. The 6600 came with around 104, even the small 3300 had 70 to run it. Only combine that had around 50HP to run was the 45 and 40 combines. By the time the Titans came around not 1 combine had under 100HP. PTO combines requires just about the same. The tractor has to run it and pull it.
However yes around 50HP could run it. Just sitting in the yard doing nothing.
My 6601 will be pulled by a Model 9600 Ford tractor. I know that's a bigger tractor than actually required, but it's one I have ready access to on my vegetable farm. I actually found 2-6601's last fall, but just waiting to get them moved, unless a fellow collector gets them first.
20 years ago we had a 4440 on a 6601 its a perfect fit and yes its about 130 hp.A tractor 45-55 hp if fine if you just want to turn it over to check it but you may actually want to put some crop in the front.Even a 4440 we killed the engine lots of times when crop got a little heavy.