Here are the gear ratios I know of the C5x and C6x (6 speed) transmissions. As mentioned, I have a C52. Mine is from the 7A-FE, so it has a taller 1st gear than the 4A-FE C52, and lower final drive than the 4A-GE. All have a .815 5th gear though, and the final drive will be replaced with the A244's gearing.
If that is not enough, I'll could always try to get my hands on a C59 which has a .725 5th gear ratio. That would bring my rpms down to an almost ridiculous 1360 rpm at 45 mph, or 1960 @ 65 mph. I'm thinking that that is a bit too low though. However, the C65 would probably be a perfect match as it has a .815 and .725 gear. But, those typically cost a ton and are pretty rare.
