Jack makes a few upgrades for the D20, his gears are cryo treated ect. Give him a call, he is a real nice guy. He will send you all the paperwork on his parts.
By all means, give Jack a call. But block out about an hour or so, 'cause he does like to talk.
I always wondered why the vendors only sold the 4.86 Jeapeater gears. Jack has a full range of gear ratios available for the Dana20. Plus he stocks all sorts of replacement parts for the Dana20, like rebuilt shift forks that are squared to the shift rail and have the wear pads at the sliding gears remaned back to factory specs.
Jack is a metallurgist by trade, with a long list of credentials. His gears are manufactured using a completly different process than the stock Dana Spicer or Teralow gears, and if I remember correctly, are about 1.5 times the strength of the other available gears. As the saying goes "You get what you pay for." It all a question of whether you need it or not.