I have a friend that has a F106 rear axle for sale in stock form. It has a 6:20 gear it came out of a 69 or 70 5 or 600 series ford if he remembers correctly.
$600. Call me at 641-919-4664.
JT, the 6:20 gear one is sold but he is checking ratio on a couple more he has. I will shoot you a message when I know what gear they are for sure. I hope to know by this weekend.