I was wondering if it is possible to change a inline 6 out of a 1991 Ford F-150 and but in a V-8???

 

It certainly is. I am building a 351 windsor right now to take the place of the I6 in my 1992 F-150. You would need to weld in some new motor mounts, but it's not any harder than putting a bigger engine in any hot rod. Just measure, test fit, weld, and drop it in. There are a few people on another (Gasp!!) message board that have done the same swap succesfully.

-Jon