A few more ramblings.......

Looking at Jim's 424 combo above, the "other" motor wasnt really all that far off as far as peak hp goes, if you look at the hp/ci.
Using Jim's 603hp and 424ci, it's 1.422 hp/ci.
If that 410 made the same per ci it would have been 583hp.
Since they saw 567 out of it with a carb spacer, that's 1.382 hp/ci......so, not "way off"(16hp).

My gut feeling is, whatever is making it so the low end TQ is so far below where it really should be...... You fix that..... It would put up a better number up top.
I see it pretty often........ Start low/end low.