318 upgrades

Next dumb question is ; what's the best/easiest/cheapest way to lighten my 75 dart-Swinger by 15%, so that the 318 will perform like she be 15% bigger.
It's a trick question; best /easiest/cheapest, as it applies in this context, should never be found in the same sentence.
Fiberglass front bumper with aluminum brackets, gut the interior, remove HVAC, radio, convert to manual steering and non-power brakes. if you have some money left over: fiberglass lift-off hood (with a scoop is almost free horsepower). Oh yeah, scape all sound deadening and undercoating off.