First, welcome!
As for the problems, are you
sure you have a 351W? That engine didn't come in a Bullnose truck until '81 in the California trucks and '82 in the 49-State trucks. On top of that, it never came in an F100. But you may well be correct as the W got swapped into a lot of trucks, especially where a 302 had been since it is a fairly easy swap.
However, the source of the engine or transmission may well be the issue with the starter. Looking at the starter listings from Ford's master parts catalog (Engines/
Starters), something changed as of 4/80 that required a different starter, and then on 12/83 something changed again. And, looking at flexplates (Engines/
Flywheels), the 1981 351W's used a different flexplate/flywheel.
So I'll guess that you have a mismatch in starter and flywheel.
Oh, and you do know that a manual transmission starter won't work on an automatic, and vice versa. Right?
Gary, AKA "Gary fellow":
Profile
Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI