Front driveshaft diameter

[Short 3/4]

When I assembled the truck way back when, the thicker of the two shafts was dented, so it got scrapped and I used the thin one. The splines are now completely worn out. Since it sees a fair amount of off-road miles I want to build a good reliable new one I won’t ever have to worry about. The 3/4 ton 64 I got the running gear from did not have a front driveshaft when I got it and I have never seen another 60-66 K20 in person to check out. The few 60-66 K trucks in my area I’ve found are all 1/2 tons, and all so far have the smaller diameter shaft. Can’t remember where I originally got the larger diameter shaft, as I was doing a lot of 60-66 K truck parts scrounging for many years before finally assembling my truck.
Thanks for any help,
Tom