Gearing question

[silversvs]

I got the '59 all put back together and running. She runs like a top but my gearing is way to high. I have a sbc 350, Muncie M21 4 speed and Ford 8.8 posi with 3:73 gears. I'm winding the motor up too high even at 55mph. I want to keep the 4 speed so I'm looking to drop the rear gearing. The lowest I found so far is 3:08s. Anyone have a way to calculate how much of a difference the gearing combination would make? I'd like to only make this change one time. Anyone know if there is something lower for the 8.8 like a 2:70 or 2:92? And anyone point to a retailer with good pricing? Summit only has 3:08s at about $170 a set.

Thanks!