Well a junkyard jewel 360 is going to require going into the motor to get 400 HP. The crate 360/380 HP motors have higher compression pistons and a hotter cam. So basically you are talking about a rebuild so you are looking several thousand dollars.
The Crate 360/380 and 360/390 are magnum motors and have 9.0:1 compression ratio and a stock magnum 360 has 9.1:1. The LA 360 was around 8:1, The crate does have a hotter cam but a junkyard 360 magnum is going to give you the same comp./ratio