What size Holley 4150 or similar for engine?

Thank you. I just wanted to see what CFM Holley would work in case I see one for sale. I really like the Thermoquad design as I feel it was a design way ahead of their time. I actually have 2 TQ my backup is on the car now as the one I had setup for the engine won't even idle the car. In case I can't figure things out I would lean more towards the speed demon as it seems to be a TQ but easier to work on.

After a long hiatus of barely touching the car, my fault the Demonsizzler carb not working now, I'm finally back to working on the car. I've cleaned my Demonsizzler carb and will try to see if I can't do something to get it working right again. If I can't I may just move on to something newer. That is why I'm asking what CFM Holley and if that Speed Demon would work. I'm glad 750CFM can work as that is usually what I see for sale locally.