As long as it shows it as an F150 I wouldn't be bothered by it. Cab swaps are pretty common around here - I had one all lined up before I shipped Camano in from Dane's neck of the woods. Just sold that cab and title a couple weeks ago actually to a guy doing the same.
It's definitely something a prospective buyer should inquire about though as if done wrong, could lead to a hassle.
Scott
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Camano' 1986 F250 Supercab XLT Lariat 460/C6
'Chanute' 1980 F350 C&C 400/NP 435 - Gin Pole
But there ain't nothin' wrong with the radio