My dad can afford either choice. I think he is trying to stay $3K or under for the engine. His stang will be a weekend cruiser with the occasional spanking of his kid and his big mouth (me).
He wants something fairly mild, if a 429 or 460 can be called mild. He is not looking for a lopy cammed motor. He wants something with a little lope at idle and something that can scare the neighbors when stomped on. Originally he was thinking about 400 HP/TQ with his 351, but then started thinking what would a 429/460 be like? Personally I like his thinking.