Dana 20 speedometer gear change

I found a number of "calculators" online that tell me I should have a

31 tooth gear for 33" tires and 3.73 gears. Some of these also included a list of part numbers that should work at a Chrysler dealer (31 GREEN 52068153). These part numbers seem to be linked with discussions around the Dana 300 T'case. Would this be the same gear in a Dana 20? Is there someone online selling the gear I need?