360 with 350-400hp, 6,000 RPM- what does it take?

Im not sure what years the 360 had the roller cams. I would say mid late 80s till 94 when the Mag. came out. The Magnums use a different intake so you either have to get the correct one or redrill the heads to use the LA intake.

The issue with Magnums is that the heads are always cracked. It doesnt seem to cause a problem but Im not sure I would put money into a motor with cracked heads. You can get EQ Magnum heads that are already drilled for the LA intake for around $800 LA motor mounts and trans bolt right up..