Seems a little slow...

Put the 750 back on with the four hole spacer and work with the carb.
You have a good converter and enough gear to run the bigger carb.
You lost 4 mile an hour with the 650 carb.
I would put the pinion snubber a half inch from the floor so it works.
The weight of the car gets pushed up, by the snubber hitting the floor when you take off from the line.
You want that snubber to stay in contact with the floor as long as possible.
Making the snubber closer keeps the two working together.
This is what pushes the tires into the ground for traction.
I think the only problem you had, was the 60 foot times needed to be improved.
Get the right set up into the 750 carb and keep the snubber close to the floor.