Just trying to eliminate possible causes....I had similar starting and running issues with my car (4129), with approximately the same mileage as your car...especially the dying at 40 mph...I have a similar engine set up with the exception of my Mallory dual point ignition...my problem turned out to be the feed line from the gas tank to the fuel pump. Under close inspection it had fine cracking in the rubber, almost unnoticeable...the line wasn't leaking, but apparently pulling some air under load, causing the Holley to stumble and die, or restart and run fine for brief periods of time....an easy thing to check...
If you have stainless gas lines, then obviously not the problem...
good luck...Pappy