[Joyridin]

I put soapy water on the floor under the tire (heavy on the soap). My alignment gauge says 15 degrees left, then 15 degrees right. I usually put tape on the floor at 15 degree marks.

I am not sure how accurate it is, but caster is usually a pulling/handling issue, not so much a tire wear issue. So as long as it is close and goes down the road straight without pulling, you are probably pretty good on these old trucks. If you are racing it, might want to take it to a shop.