Definately. My tank is only a 20gallon high, so a single PH connected to 2 2L bottles works great for me. Your tank is more than twice as long as mine, I would if you can have one on either end at substrate level...
EDIT: This is your 75gallon tank from your sig correct? How on earth are you getting 65ppm CO2 by DIY. Can you tell us where you are taking water from to measure CO2 levels? Right next to the PH, on the far side, what depth level? You're the perfect candidate for pressurized, but I like you, hate the cost issue. Think I'll be treating myself to a pressurized system this Christmas however....