400 to 475hp is gonna put you in the 502cid range for a crate engine. Scoggins-Dickey, or Pace Performance is the place to buy a GM crate engine. I have found that the prices are all very close on a given engine, shipping is where they really get to you. When I bought my crate engine Jegs wanted $179 to ship it. Pace shipped it for $49, they had a special on shipping going when I ordered it. I don't know what the shipping is normally...good luck.