A500/A518 Aftermarket Overdrive Ratios

Hi, working on installing an A500 behind a 318 with 4.56 gears. From what researched I gathered the standard ratio for the 4th gear overdrive is .69. Did mopar offer vehicles with a better ratio lower than .69? I saw the gear vendors unit is .72 which is higher.

Are there any aftermarket gear sets available for these transmissions to change the ratio?

Thanks!!