My trip to the track...

Nice wheels!

There are a bunch of things you could try.

Change preload on lifters
Fuel system upgrades, fresh lines, fresh filters.
Metering block in rear of carb and jetting
A lighter vacuum sec spring. Softest until it bogs at WOT application, then up one in stiffness.
A 750dp carb would really make a difference
Timing curve - all in by 2500ish and keep feeding more total timing. With pistons that far in the hole, it's more like an open chambered head. Open heads usually run more timing. You may get into the low 40's. Test test test!

It appears soft on MPH for what the set up has in it. The ET at each incremental point doesn't appear that far off, that's soft most of the way through. Strangely, the MPH at 660 is strong for the ET. Those are some confusing timeslips.