Pull the cover and look at the ring gear. Somewhere along the edge you'll find a series of numbers. Two of those numbers are for the teeth on the ring and pinion gear.
My GM 12 bolt has the numbers "7 GM (six numbers) 11 41 s 02" stamped on it.
11 pinion teeth to 41 ring teeth means a 3.72 ratio.
Good luck!
'51 Chevy 1/2 ton w/'62 261, HEI, offy, fentons, dual carter/webbers, t-5 & 12 bolt posi
| 
