Hmmm....3.55s or ???

My 68 Cuda has a 318 .030 over, with a 4-speed, 3.23 gears and suregrip. At the track I'm averaging about 15.85 1/4 mile. 60 feet times are 2.35.
Any idea what gears I could put in to get my times down to high 14s?
I know this is a silly question, but I wanted some input from you all.