[Bill Baer]

I agree with Bob, weight is simpler and more predictable when your that close to the index.
I have a home made, inline air (Co2) cylinder stop and it's a pain in the *** because there are a lot of variables stroke length, stroke time, the amount of resistance,in the carb linkage, Co2 Pressure, how solid the throttle pedal stop is, how much stretch and slack in in the throttle cable.
Ballast is the simplest and cheapest but there a couple of other ways too, Moroso markets a fixed stop and there's some guys selling a restrictor plate system which would work too also if you using a vacumn secondary holley or demon you can put a stop on the vacumn motor.
But if your determined to build you own in line stop contact me and I will help you with it.( But I can almost guarantee you, at some point, it will drive you nuts!)