Nothing wrong w/ the parts list IMO. Definitely something stupid holding it back. The lifters could be an issue, but there's no reason a hydraulic shouldn't pull to 6k+ rpm. Might need different lifters if those are bleeding down. A solid roller would be my choice too, but the hydraulic you have should work.

Check things like where the cam is in at, verify the TDC mark on the balancer is where it should be, verify you don't have lobes going flat, etc.

FWIW...my old stock stroke 440, 10:1, basically stock 906 heads w/ the 509/292 purpleshaft (w/ stock stamped rockers and stock pushrods) made 340 hp on the chassis dyno and ran 11.80s at 112 mph at 3700 lbs.