A 37 fourspeed would have about the same ratios on the top three gears as your three speed with a creeper (granny) low gear which is only used when you are starting out with a heavy load or for creeping through a hay field, unattended, while you buck bales. Two disadvantages to it are that it is a crashbox (no syncros on any gear) and it is very heavy. You could use the later version of the early fourspeed that has syncros on the top three gears. The only close ratio fourspeed I have seen adapted to the torque tube is a Saginaw with a kit from patricks in Casa Grande, Arizona. Its disadvantage is that it is a side shifter, not a top shifter.