Howdy Bruce,
The 404 tranny is 6 foreward 2 reverse. The engines are the gas engines m 180 & m 130. The 180 has 90 hp & 120 ftlbs of torque. There has been discussions about the ability of the tranny to handle sustained speeds over 55 without damage. If you want a Mog with a diesel look at at any other model. The most popular is the 406/416. G-Man can comment on them better than I can. Adapting any Mog tranny to a non-Mog frame would be a major job. As they say anything can be done with time and money
As for sources you are in luck. The one website you need is
www.rockymountainmoggers.com/unimog.html
Go to the Mog links and look around. Several Mog dealers are; Michael Smith of unipaser, Sean Philyaw, Chris Elliot & Scott Ingham. Another great source is Eddie Runners Mog mailing list. I am trying to bring some of the people in that list to this forum. (so if you go there don't abandon us
) Hope this helps. Good luck in your search.