I just had a thought. Figure the first gear in your 3-on-the-tree is going to be like the 2nd gear in your T18, 2nd gear would be like the 3rd gear, and 4th would be 1:1.

The T18 is a 3-speed with granny low, same with NP435. The ZF 5-speed is a 3 speed with granny low and overdrive. the 3-speed part doesn't change with transmissions, the split is *roughly the same. Now an M5OD is a 4-speed with overdrive, and there are Toploader 4-speed overdrives, basically a 3-speed with an overdrive.