Ran 10.5 index Saturday...made it to 6 cars....

I think a 4150 carb with a 1.600 venturi is going to be a challenge to get bog/hesitation free on a small block foot brake combo........ but I’ll keep watching to see how you go about trying to sort it out.
You are probably right. I'll let you know if I find a consistent way to make this thing behave itself.