I see, I have been picking around looking for a 3spd aux myself for a load star project.
then I stumbled onto a school bus to haul my small snow cats, the bus came with a parts bus...... ( why wouldn't it ) the parts bus has an allison that has a seemingly tall final drive. I have now decided to ditch the IH 392 gas and allison for a 24v allison with an OD.
at the winter snow cat clowder my vehicle speed sensor went missing and now the transporter moves happily at freeway speeds. My MPG are fantastic by my standard and look forward to more trips.