The NP435 was produced with at least two different ratios;
4.78-2.39-1.37-1.00 splits of .50-.57-.73
6.69-3.34-1.79-1.00 splits of .50-.54-.56
That granny gear is NOT synchronized, which means it takes a trick to get back into it, on the downshift. Without it, second gear might be a bit of a stretch......
Corrected to a 24" tire, the second gears math to
4.10 x2.39 x24/33=7.13, and
4.10 x3.34 x24/33=9.96
OOPs I guess not,lol. At least not for the engine you are building.
