An F100 w/ 105 that you can't confirm is a 105?.........................Just on the surface 105's were made in the very last years of FEs. I believe they only got installed in trucks because FEs were no longer in cars at that time. So were talking 72-73 and up. What stumps me is were F100s even being made/offered that late and if so FE V8s in F100s? Anyway other then the numbers on the underside of block there's no assurance of a 105. Odds are good someone swapped out a motor block so dig through the grease. You know the key part of 105s is the crows foot webbing on mains. FECA years ago did a poor mans CJ and went through five 105s to find one that bored to 428 safely. Lot of $ until you look at price of 428/CJ