Re: Need 4:10\'s for a 12 bolt
I believe 4.10 werent in 12 bolt.....
but 4.11 ratio was available from factory in at least 67-72, But are VERY rare to find an example of, have only found one in a '68 suburban in NH just recently
Tthis 4.11 ratio was incuded when RPO M20 O/D transmission(SM326 saginaw 3 speed manua with rear add-on .70 overdrive ratio final drive unitl) was ordered in these trucks.
Maybe possibly was 4.10 in later years such as 76 or so til 82(82 last year of the 12 bolt axle) but I dunno about that possibility.... 4.10 was mainly or only a 3/4 and 1 ton ratio.
I feel you wil be going for aftermarket gear set to get 4. anything ratio in the 12 bolt
just making notes
good luck