Well, here's what I did and what happened.
Connected a hose (3/8" fuel hose, to be exact) to the radiator petcock. This hose was slightly too large and leaked, but only very slowly (drip.... drip... drip...). Drained the radiator and ended up with ~3 gallons of coolant. I replaced the upper radiator hose without issue, maybe 1/4 cup was trapped in one of the bends, and I used a tupperware container to move that to my drain container. The lower radiator hose held quite a bit more... several cups. That just spilled everywhere... oh well.
I once I had the new hoses put in, I tried running the engine for 30 seconds or so, thinking that perhaps the pump would move the engine coolant into the radiator where it could be drained. This was not the case... nothing new in the radiator. I didn't want to overheat the engine so I turned it off. Re-filled the radiator with the garden hose and by then it was dark and I was late for something, so I decided to continue with the flushing another time.
Question... according to the CUCV wiki article, total capacity is 25 qts (=6.25 gallons), so I take it either I was extremely low (didn't look that way based on the reservoir, which was about 1/2 full). OR, the engine holds about 3 gallons of coolant on its own.
Tomorrow (or maybe Tuesday... my next day off work) I'll continue flushing it out, which I suppose looks something like.
1) drain radiator.
2) fill radiator with garden hose.
3) run truck for several minutes.
4) repeat until step 1 comes up clear.
I had bought a bottle of "Radiator Flush" ... stuff... anybody think this is a bad idea?
Feels so good to have another few crackly rubber parts replaced with all brand-new stuff!