I stand corrected... gear venders has a .78 overdrive. Us gear uses a .8 overdrive. The NV4500 a .73 overdrive.
Not trying to favor any overdrives here, just trying to give you some info.
You will need a new speedo cable for the gear venders OD.
The SM420 has a 7.05:1 1st gear. The NV4500 has either a 6.34:1 (early chevy) or 5.61:1 1st gear.
Most NV4500s... early chevy excluded... are fully syncroed. The SM420 is not syncroed from first- second.
