Have a 1984 Ford F150 w/ 460.
Has been running great, but now won't start even w/ a jump.
Had battery checked and it's fine.
Replaced starter and still won't start.
By-passed selonoid and attached cables from battery to starter. Still won't turn.

Ideas to try next? I'm going to take the new starter off and try it just w/ the battery to see if I got a bad one (again).

 

Just in case you overlooked it, what about the solenoid on the R/S fender well?
If the solenoid is defective or it has a poor ground due to rusty mounting, the solenoid can't/won't work. That solenoid is what energizes the starter when you turn the key to the start position. Also if the ign switch is no good the solenoid can't work.
Would pay to check before removing another starter.