440 /super charger add on ?

You'll need to consult some charts for reference, either on the BDS or Dyers site. There are many factors you need to compare to arrive at an appropriate drive ratio: Engine displacement, static compression ratio, blower size (6-71, 8-71), dynamic compression ratio at a given boost level, etc. The pulley combination (or drive ratio) affects how much boost you'll potentially generate. Too much, you grenade things.

In a nutshell, with a 6-71 on a 440 you need to overdrive or spin it faster (bigger pulley at crank, smaller at blower) to make boost. An 8-71 moves more air per revolution so it doesn't need to spin as fast. So, if you put the smaller pulley on the crank and the bigger one on the blower it will spin slower or be under driven. If you swap pulleys it will be over driven by the same amount. If you do the math, the difference between the two pulleys you have is 8.3%. So, installed correctly, you can under drive your blower by 8.3%. Whether that will give you the safe and sane boost level you desire, you'll need to determine.

You have some homework to do.