Finally fixed. So, it has been almost a year and just recently I had some time to look at the car again. I am fortunate enough to have another vehicle which I have been using. I went as far as turning in my tag and took insurance off knowing that I would not be able to address the issues for a while. Just to recap it's a 91 740 with rex regina fuel system. This system uses one in tank fuel pump and there isn't a check valve. I searched the internet and found a few hits regarding the situation, and it turned out to be the little device that is connected to the output of the single in tank pump. Some folks refer to this device as an accumulator/ pulsation dampener/ pillow/ mini vintage ford brake master cylinder cover. It is no more than 2 inches by 1 inch and the metallic top has a detent hence looking like a pillow. I removed it, essentially bypassing it with a length of submersible fuel hose that I purchased. (28 bucks for 12 inches) The inner diameter was 5/16 inch. Owners who did this fix reported driving thousands of miles without any issues. No more hesitation, backfiring, and the car starts almost immediately like it did before. It will be my beater car. Prior to problem I installed four new shocks, a new radiator, center bearing, cone bushings and a new cam and cam sprocket from IPD. New crank position sensor too. Time for insurance and getting a new tag now.