You may have the wrong impression about parts oldschool....
A yellow spring IS NOT going to make any thing faster. It'll just hold the "gear" longer, helps going up hills....
A multivar MAY get some extra on top end(another seemingly never ending debate) some claim 4mph on top end... I didnt get anything really.. It does help the "shifting", makes it smoother, better.. The ramp plate is different than the oem to aid the roller travel.
Even a bbk will only net about 5mph but the torque is a different story, it'll get you there quicker.