ApacheFiend,
I can't offer anymore advice because I don't know if your spindle bushings are suppose to be a press fit or not. The comment from your book about lining up the hole in the spindle and bushing would lead me to believe that these are a press fit...otherwise they would move around at will.
My "guess" would be that if you have 'new' bushings that push into your spindle bore by hand, then your spindle bore is worn oversize.
This is a guess. Actual assembly instructions are needed to determine if this is fact or fiction.
Whatever the story is, your spindles are not junk so don't dump them.
EDIT. The '55 2nd shop manual indicates 1/2 ton trucks use the floating bushings...again, don't know about a '58.
Stuart