^^^ Yup - 1st question: bias ply tires ? They'll follow any ruts or uneven surface.
Night & day difference swapping bias to radial with no other changes.
As for the aftermarket upper arms, I haven't found them necessary for my street cars using radial tires.
Generally, more caster will be better to drive straight, and I try to get about 5 degrees with the stock stuff if possible.
FWIW, my drag car had Jack Arnew's altered OEM upper arms (widened), and about 7 degrees caster, and it went straight as a string even on bias plies.
The steering wheel would unwind with a vengeance after turn-outs, but no biggie vs stability @ 130 or so.
That said, it was never street driven, and track vs street surfaces differ.