Velocity stack are "tuned" via length to the frequency of the engine. Using the wrong length stacks will not only not help performance, they may hurt performance.

Do a baseline with no stacks, then run tests after installing the stacks to see if they helped, hurt, or no change.

Jon.

Good carburetion is fuelish hot air
The most expensive carburetor you will ever buy, is the incorrect one you attempt to modify!!!