I believe any competent engine rebuilding shop should be able to help you out.
It's not like the 6 cyl is any different than building most standard engines.
Just need to check for clearances, basic blueprinting skills.
And since you are looking to make monster power, there is more leeway in building a almost standard engine.
Bump up the compression a bit, a mild cam, & mild head work & it sounds like that will good for you.
MBHD
