Before anything, follow the advice in the first two posts. Make sure the front end is in good condition and try to find someone that knows how to make changes to caster and camber if needed. Caster adjustment requires tapered shims at the axle. Camber changes require bending the axle!
Also, consider installing a front sway bar. I'd start with one from a YJ jeep, 87-95 Wrangler. Getting rid of the rock n roll will make that truck drive very differently.
With that said, I will vouch for better steering with 3600 steering arms. I've posted a
video of the LH 1/2 ton steering arm flexing and I've installed 3600 arms on my 3200 1/2 ton truck. Noticeable differences include better steering accuracy (the truck goes where you steer it) and less steering input required while driving.
I spent a long time watching Ebay for the parts. I would search for part numbers as well as searches like "chevy truck steering arm" or "gmc steering arm" and look through thousands of results. I would limit the results by including a year or year range in quotes. "1957" chevy truck steering arm gets very different results than 1957 chevy truck steering arm. If it helps, LH arm part numbers were 3667727 and later 3713017. The only RH part number I have is 3728383.
The steering arms will bolt right to the spindles using existing bolts. My 3200 drag link fit the 3600 steering arm with no issues. I also re-used my 1/2 ton tie rod ends which required getting ball studs to mount in the steering arms. I purchased
these studs and was ready to purchase the
TRE rebuild kit if needed. The toe was significantly changed with the replacement arms installed so I had to make some crude adjustments to drive home then I paid a local shop for a "toe n go" alignment later.
The next step for me will be rebuilding the steering box, or at least trying to replace the output shaft bushings. 67 years of wear does add up.