Until the question about just how the converter is behaving is answered......it’s a little hard to gauge the effectiveness of the cam.

I’d say if the 60’ was noticeably worse foot braking vs the transbrake, then the cam and converter may not be on the same page.

The car performance is so far off the dyno numbers of the motor, it’s hard to know what to look at first.
But that test might be revealing.

Be nice to see a dyno sheet to see how the curve looks.

Using my 90% rule....... at 880 STP corrected HP, it should be running 10mph faster.

The 140mph is showing what works out to a 28% loss.

It hasn’t been mentioned, but I’m assuming these runs aren’t being made at a higher altitude track.

One other thing..... does the car roll easily?
No dragging brakes or trans binding up?

I guess if I had to start somewhere, I’d see about borrowing a known good carb and see if anything good came from that.

Do the footbrake vs trans brake test.

Then look at those results and see if it makes sense to try a different converter.

If after all that it was still showing way low on power, I’d have the motor tested somewhere else.