i did underdrive pulleys , equal length headers , 3.55 gears , and dropped about 80 lbs. off of the weight of my 90 mustang notchback and I went from a 14.2 to a 13.6 in the 1/4 mile with street tires . These mods are all fairly inexpensive. Check out this site , they gat pretty cheap prices on mustang parts.
www.neweraperformanceparts.com