505 stroker fresh off the dyno - Power seems low? Thoughs?

You’re getting a lot of info, some of it conflicting, from several sources....... so I’m just going throw a few things out there...... and hopefully not add too much noise to the conversation.
Those springs are a PAC-1903.
I just had a set of those TF240 heads here to look over. They had that spring package and they were set up right at 1.900” installed height.......115 on the seat.
The spring rate is 391lb/in.
Your gross lift you stated as .575” lift...... minus lash puts you at roughly .560” net lift at the valve.
391 x .560 = 219lbs, plus the 115 on the seat = 334lbs open.
Imo, nowhere near enough for a BB bracket race engine with a fast rate cam.

My guess is, Hughes sells more cams ground using that family of lobes from Howard’s than anyone.
Look at the spring specs they suggest for a BB using those cams.
Also, look at the specs for the springs Howard’s recommends(98632) for those lobes in a BB.
Calculate the open load at full lift for that spring if you were running the 720162-08 cam(I’ll give you a hint...... it’s a fair amount higher than 360-370).

The low-ish spring load isn’t a problem(rpm wise)....... until it is.
Was that contributing to the early power peak of your engine?
Hard to say.