1) is there a special steering fluid that i need to buy for this unit?
I believe the original spec was SAE 20 non detergent, non-foaming oil, so a UTFH should be fine.
2) if i loosen hose , coming from pump, how much fluid can i expect to come out, when engine is running. provided that pump is o k. ?
Depends on how much you loosen it but likely more than you want to deal with.
3) are the hoses likely to be causing a problem? sometimes an old hose will deteriorate, and insides can cause a problem.?
Hard to say if a hose or hoses are causing the problem. Yes, an old hose will deteriorate, and insides can cause a problem. I have had improperly made new hose cause problems as well. You would need to remove and inspect them to know for certain.
4) i loosened the line that goes from the pump to the torque ___ and started the engine. no flow of fluid. so i presume that the pump is faulty , or something is blocking flow of fluid from reservoir to the pump .
Is the reservoir filled to the proper level, given you are asking what oil to use in it? If the reservoir is mounted above the pump, do you have fluid to the pump inlet from the reservoir?
5) is the power steering pump, an easy re build? are parts available?
I don't think it would be a hard rebuild, if you can get parts. You will need to check with an AGCO dealer that will chase AC parts to see what if anything is available and/or your local hydraulic shop that rebuilds pumps.
6) the steering worm gear, probably needs lubricating. how is this done? does the radiator have to come off to do this?
The radiator does not have to come off. There is a cover you remove and the oil level (SAE 140 or SAE 250 depending on the front axle it has) should be about a third of the way up the gear. That info is in the Operator's manual.
As I posted before there is some service/repair info on the unit, like the one in the video you referenced, in the service manual for the WD, WD45, and D14, AC part number 79003405. The current printing of the WD operator's manual part number is 70257977. There is a copy of the original WD "Operating Instructions and Repair Parts Illustrations you can download and save at:
https://www.manualslib.com/manual/1841723/Allis-Chalmers-Wd.html. The parts book says it was used on the WD45, not the WD, so a current copy of the WD45 Operator's manual part number 70257975 might have the info on the fluid for the power steering unit. I am assuming you have verified you have a WD, not a WD45, by the serial number. Investment in the manuals may help you.