Only 460hp

This is a little reminder worth mentioning periodically ………

And the gist of it is when you have an engine that’s making less HP than TQ, it’s because it’s coming up short in its ability to carry the TQ curve high enough, and/or fall off slow enough for the math to work out favorably.
There’s not enough of something airflow related……whether that’s the carb, intake, heads, camshaft, or a combination of several of those items.

That doesn’t mean there’s necessarily anything wrong with the build, it just depends on what the intensions for it are.

The dyno sheet for the OP’s build shows over 500ft/lbs.
Address the things that contribute to the curve falling as fast as it does…….to flatten it out after peak TQ, and you’d be well on your way to 500hp.

I’d be shocked if those MP heads flowed anywhere near 275.