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Did you rebuild your drag link and tie rod ends? Are you running fairly narrow radials - in the 215 range? Is your steering gearbox in good condition. These are the most likely culprits.
Leaf spring bushings
Wheel bearings
King pins and bushings
Drag link innards
Tie rod ends
Steering box sector shaft bushings
Steering box worm and sector gears
Steering box shaft bearings
Hmmm - sounds like between the two of you you've hit most of the usual suspects.
If the front end parts mentioned are all in good shape there's also a steering stabilizer/dampener available to control bump-steer. It looks like a shock absorber that bolts to your I beam axel on one end and the other end bolts to the tie rod. LMC Truck advertises them but there's probably others out there too.
Rick, welcome to the board. I only drove my 49 a few miles before tearing it apart for modifications but I know what you mean about wandering around. I once drove a 68 Ford F-100 with the twin I beam set up that was so worn I got pulled over once and was made to do a drunk test, after that I started replacing front end parts.....lol
Good luck with figuring it out. You'll get tons of great advice around hear as there are many fans of the stock front suspension
Try setting your front toe in to about 1/4" - the closer the tires are to pointing the same direction the more it wonders. We set our heavy trucks for a 1/4" in toe in, and our 1/2 and 3/4 ton trucks for about an 1/8 inch. More than 3/8 inch will cause the tires to scrub.
Of course, better to replace worn parts, but doing this will help.