70 Duster runs rough or dies when up to operating temps

It is not a fuel pressure problem. The Edel fuel system is an EXACT copy of the original Carter AFB fuel system & Carter recommended 7.5-8.5 psi for performance applications. The Carter float level chart goes to 10 psi. I have personally run 11 psi, zero problems. The float leverage system on Carter/Edel carbs is well designed for high leverage on the float needle BEFORE flooding would occur. Further, the Edel carbs use the smaller 0.093" n/seats, where some AFBs used larger 0.101" n/seats. The smaller the n/s seat, the more pressure it can take before fuel pressure overcomes it. If somebody would like a copy of the 10 psi chart, pm me an email address.
For the umpteenth time, Edel specifies a 5.5 psi pressure because that sets up the fuel level for their 7/16" float level as a datum point for the correct a/f ratio with the jets that the carb is built with. It is NOT the max pressure that can be used.
The Max Wedge & Street hemis used Carter AFBs, exactly the same float system as the Edel carbs & they came with 6-8 psi pump ratings.

Run the engine again at idle with the timing light hooked up to the coil lead so you can watch the flash. When it starts to fumble, see if the flash rate changes; this might be hard to see but could give a clue if the problem is spark loss.