dont take this as gospel, but your best bet might be a wrecked RV/Mobile Home or perhaps an old super duty pick-up/dump truck/etc. I know the last time I was at the yard, all I saw were 5.0's and 351's in the older pickups. Sadly, a lot of the 460 cars have been scrapped already...you might get lucky and find an old Lincoln (70s vintage) or perhaps a marine motor somewhere for a reasonable price.
By the time you are done with machine work (unless you work at one or have a hook up) you might be better off buying yourself a short block or building a 351 stroker.
Good luck!