Both the 6 and 8 also have a different bolt circle diameter than our "5" ?
What's an 8? Did I miss something during the conversation and someone's got an 8-bolt spindle? Or are you referring to the wheel bolt pattern?
Given the members in this discussion, an 8 on 6.5 wheel bolt pattern is a definite possibility!
For spindles though, the 6-bolt drum spindle absolutely has a different diameter and register depth than the larger 5-bolt disc spindle.
Just not sure about an 8-bolt spindle if that's what you meant.
Not sure which '79 spindle reamer is referring to either, but normal F150/Bronco disc spindles should be the same 5-bolt version as the '76/'77 Bronco disc spindles. Might have offset holes, but there are only five. Well, at least that I was aware of. As usual, open to learning more about, well, just more.
Be interested in hearing more about both!
Paul