Imo, if you set out that build a 505” 12.5:1 “bracket race motor”, to run in the 10.00 range....... you built the wrong combo
I’m not saying you can’t get there, but you didn’t hit the “easy button” with the combo you built.

It should have been done with MW heads and intake manifold, 4500 carb, bigger cam, and more stall.

The std port heads will tolerate way more cam than you have now, but you’ll likely need to run more stall to really take advantage of it.
If you’re racing through mufflers that needs to be taken into account for cam selection.
I can’t see the motor picking up 75hp with a cam swap.

Bigger cam first, then a stall adjustment if necessary.........and in the mean time I’d try and pick up a 337 intake manifold.
Get the manifold port matched to the full MW size and open the heads up to that as well.

The best shift point is usually dictated by the interaction of the motor and converter....... so some experimentation is normally req’d to determine what the best shift rpm is.
Off the top of my head, I’d say somewhere in the 6000-6200 range.