I also own a Ford 850 TLB as you owned a 641. My loader works off of a rear pto pump with a power beyond back to the 12' backhoe. Kinda generic way to do this but it is functional to some extent. My PTO is "dead" (unlike your 641) so to further complicate the setup, everytime I press the clutch, all hydraulics STOPPED! OK, it sucks, thats why I bought something 60 years newer. (06' dk45s). But anyways, what I mean to point out is: They make a coupler that hooks up to the crankshaft on one end and it "shafts out" to a lovejoy coupler which in turn drives a vane pump. There is no need to have a clutch for this purpose because vane pumps operate by centrifical force, i.e. there is not much pressure built while turning the engine over, most pressure is built once the engine is running. Thats why your loader on the 641 worked so good. And finally, they didn't/dont just use them for a loader, they utilize the pressure/extra driveline for logsplitters,generators,immobile sprayers and water pumps for farming and such. Try to remember, there was a day when 3 bottom plows were very difficult to take off of the 3 pt's. Or any implement for that matter. Thats why quick d's and quick hitches have become such a Godsend for small farmers. PLEASE dont pick on PTO's that run at engine speed, my 48' CUB performs such a task....flaulessly. These machines were disigned for a task and they STILL perform these tasks even 60,70,and 80 years later.