I've been in your same situation searching for solutions to stumbles and stops. I hope this isn't too wordy, but it may help.
For your stall out on hard acceleration I'd check your rev limit to make sure you're not hitting that. I changed mine to 7000 rpm. For my engine a little below is a nice place to shift for maximum acceleration good for 1/4 mile 130+ trap speeds on a nice day in the 70Fs or colder with 29.8 or higher on the baro. I'd also check your jet size. If you're lean it will stumble and fall off particularly in top gears with a taller tire.
When your car stumbles stopping and cornering you may have fuel slosh. You might even get fuel up over the vent tubes from the float bowls to dump fuel down the carb.
I have a similar set up to yours, Superformance 2040 with Roush 427R-095 Single plane manifold. I have no spacer, but usually run my Pro-Systems 1000 cfm double pumper set up for in line acceleration. Theeee best mod for the money I've had so far, but it's not a cornering and stopping carb.
This carb from Pro-Systems was built for track racing. I've never used it, but thought I'd share the image as it's suppose to be able to get tossed around hard with no ill effect as well as having improved mileage.
I've never had a problem with starting or fuel boil here in Arizona summers, maybe that's because of the single plane intake. One pump on the gas when engine is cold and immediate woof varoom start. Once warmed up if I'm at long multi direction stop lights I'll shut the car off while I wait. To start there is no pump on the gas and it starts immediately. If the car is warm and has been sitting in the parking lot for several minutes I hold the throttle down half way. It takes a few turns to start there, but always starts. I run the Pro-Systems 1000 cfm carb set up for drag racing most of the time.
I did throw away the Superformance supplied fuel filter and replaced it with a pop can size Aeromotive 100 micron filter. I no longer use the 3/8 inch fuel line that came with the car either. I have 8AN line and quality fittings from tank pick up to carb now. I have a mechanical self regulating Carter fuel pump. While the old line was a quality install I believed it was restrictive with some of the 90 degree bends that flattened out as well as there were cast elbows in and out of the mechanical fuel pump that were drilled suspiciously restrictive.
