I don't know where the best place would be to drill. I would start very small though because once the counterweight is too light it is going to bog. IMO - I would make sure you can get a spare easily (or have one on hand) before drilling this one. Might try the race only forum on moparts and ask there since this (to me) is more of a drag racing modification. Or if you have access to the other style edelbrock carb (Thunder series?), I think it has a spring that can be adjusted to control the air door opening rate like on the thermoquads.