There's really no need to make substantial changes to the manual steering alignment values.
Caster can only be adjusted by placing a tapered wedge under the axle. Camber adjustments aren't provided. Significant camber errors mean bent spindle or axle. Axles can be bent to make a correction. DO NOT apply heat.
Alignment specs I would keep in mind if I were doing the alignment:
0.50 degrees positive camber L and R.
2.5 degrees positive camber on the right
2.0 degrees positive camber on the left
3/32" toe
Camber window is 1.25 to 1.75 degrees. Truck pulls to most positive camber and least positive caster. Alignment tech must balance camber and caster to make the truck drive straight. Example: 1.7 degrees+ camber RH and 1.25 deg+ LH will pull right. So caster setting may end up at 1.75 deg+ L and 2.75 deg+ R to offset the camber.
If the alignment is correct and the truck still wanders then the issue is more than likely something other than alignment.
Years ago I put a 57 GMC power steering system into a 55 Chevy 3100 truck. GMC used a power steering box rather than a power assist cylinder so the setup was like what you're running. The truck was running a large set of Mickey Thompson bias ply tires. I saw first hand that the forged steering arm was flexing allowing over 1/8" movement of the drag link with no corresponding movement in the wheel. Since then I've been able to demonstrate on a number of occasions that it takes very little force to cause the 1/2 ton arm to flex.
Watch this video and notice how much the steering arm flexes. This is with a tiny amount of pressure applied to the wheel in a manual steering system. On my truck with PS and wide tires, the arm flexed before the wheel and tire even started to turn!
https://www.youtube.com/watch?v=Qlk6fzx_GDc
I'm not a superhero. If I can see this happening in the shop then I guarantee it's happening on the road.
I have upgraded to 3800 (3/4 ton) steering arms and 1" tie rod. I have added an OEM sway bar from a panel truck as well. The truck drives so much differently now. The steering arms bolt on with no modifications. My 1" tie rod was machined years ago, before you could by them, and uses stock ball and socket ends so I purchased a set of 3/4 ton ball studs to re-use my tie rod.
I haven't rebuilt the steering box yet so there's play in the bushings, yet I can drive at 45 or at 85 with ease.
I had trouble finding used arms for a while. I eventually contacted a seller that had a *bunch* of other TF parts listed on E*bay and they sold me a pair off a truck they were stripping. If you want to search by OE part number, the numbers are listed below.
Code:
1/2 ton to 3/4 ton steering parts interchangeability
Part Description Group Number Part Number Casting Number
Ball stud, 3/4t 6.243 377992
Arm, L, 3/4 6.103 3667727 3713017
Arm, L, 1/2 6.103 3711883
Arm, R, 3/4 6.103 3728383
Arm, R, 1/2 6.103 3728389 3711777