One way that I've heard of checking to see if a 460 is original is to see if it is 4-wheel drive. To my knowledge, the 4-wheel drive trucks did not come factory with a 460. I was recently looking at a 79 F150 4-by-4 with a 460 in it, just from that I knew it wasn't original, and I was right. Regardless, it sounds like a good buy, but check it over real close to see who installed the engine, and look for reciepts so you know what went into it - to see if its a new engine or a jury-rigged rebuild.