It does indeed use a 20 tooth gear with the markings as Cletis stated. It also has a shaft that fits into a 1/4" hole in the case. The gear that drives the spedo & governor is metal so I doubt that you could use anything but the correct Chevy gear.
If it is not matched it could possibly destroy both gears. Ford, Mopar, and Studebaker governor gears are all different from each other and the one you need. BW produced OD's for a wide range of OEM's but the only common thread was many of the internal parts and operational characteristics. Housings are specific to each OEM.
Fred

Last edited by rfs56trk; 07/01/2012 4:58 PM.

1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine