Plenty of simple 400hp 360 builds in articles. That's pretty much just a cam and intake swap on a Magnum 5.9.

$2500 is a pretty tight budget though, assuming a complete rebuild with quality parts and machine work.

http://www.hotrod.com/how-to/engine/hrdp-0804-small-block-mopar-engine/

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They say there is always the exception that proves the rule.
Don't be the exception.