Why is my top speed 70 mph?

a Holley 1920 on a 318 will wheeze like a trachiotomy on a distance runner. Although it would probably be able to bust them loose in first. Look into the timing and the advance of the distributor. 2 and 4bbls will still push that car past 70. it may all be ignition too if you say its hard starting. still have the ballast resistor? the rear end ratio on a one legger is a little deceiving when they are off the ground. you can do this with a buddy: paint a white dot on the driveshaft and mark a rear tire with chalk. lay next to car and use a flashlight to watch driveshaft. have buddy push car slowly while watching the tire and stop at one complete revolution (~ 6.5 feet) while you count the turns. Its going to be 2.76 or more. Thats your rear end ratio. Youll need timing light to check timing at rest (12-16 BTDC) and at 2400 RPM. It should be around 32 BTDC (vacuum removed and plugged) at 2400. plugged fuel filter will idle all day but as soon as you get into it itll start to sputter. Choked exhaust is similiar but I have never had an exhaust that was so choked it slowed the car. if the car shifts from first to second at ~30 the kickdown lever is hooked up. If it weren't you'd be in 3rd before you crossed the intersection.