[Mike C]

The motor dictated the gear usually. But sometimes other combos could affect what ratio it came with.

I've only had 350 ci trucks. 3 of them, all '72's. One Blazer 350/TH350, one Jimmy 350/TH350 and one Jimmy 350/SM465 and all had 3.07 gears. I was pretty sure the 6 cylinder trucks were all 3.73 and I think 307 4x4 trucks got 3.73 as well. But those were just the standard ratio. You could option different ratios so you would need to see the SPID on each truck to know if it came with the standard or optional gear.

It's irritating when someone changes the fluid or cover and ditches the ratio tag. Glad to see most haven't! I have an '86 K30 that lists 3.73 on the SPID that someone has lined out and handwritten 4.10. But the front diff tag was still on it showing 3.73. But when I pulled the cover to put a Spartan locker in it it had 4.10s. That is a good example of when they SHOULD have ditched the tag!