My neighbor has a 65 Mustang fastback with a 393 stroker with Edelbrock performer rpm heads . .550 lift flat tappet cam . 1 5/8 primary headers . Single 850 carb. Weighs 3200 lbs and has a 5 speed with a 4.56 gear and 28 tall tires. He runs low 11's at 119 mph in the 1/4 and turns his 6800. We talked about your combo yesterday. He knows that there is another 75 to 100 horse left in his combo with a head change and a roller cam, but he only runs his car about twice a year at Fun Ford shows. Otherwise it sets in his garage under a car cover. your et and mph tells me that your car is down on power. How old are your valve springs ? Your car can run perfect ,just not rev on big end with weak valve springs. Are they Pro Comp springs ? I have run many a big block Chevy on a 3/8 in fuel line. You need to know your fuel pressure in high gear. What is your cranking compression ? Did you advance or retard the cam when the motor was built ?