Hi guys, newbie here with rear end question

[bgood]

Guys, I've never felt this mechanicaly inept, I've read all the posts on rearend gear ratio calculations and still can't get it..Here's what i got. I have just bought a 67 chevy short wheel base step side, it has a transplanted 350 eng. w\ a turbo 350 trans. I guess its rer end is still stock with 12 bolt pattern, tire size is 275/60r/15. I'm trying to reduce rpm at cruising speed no tachometer yet but am guessing close to 2800 at 50mph (gps verified). I tried jacking the rear end up and rotating the wheel and counting the turns of drive shaft to tire rotation.
Well starting with the tires valve stem at 12 o'clock I turn it only until stem reaches about 8 o'clock and the drive shaft has turned one complete turn. What gear ratio does this indicate?

thanks, you folks have a great board here... lots of info for us challenged newbies, Bill