Saw a ad for a used G800 rear axle with the 3.42 rearend. What is this rearend 9bolt,10 bolt, dana44?

 

Looks like a deeply confused seller.

RPO codes are 3 characters, not 4. There's no such thing as G800.

G80 is the RPO for "posi". Doesn't tell what model of rear. If it's REALLY 3.42, then it's most likely a 10-bolt. Given the crappy ad copy, we just have to read what's in the white space all around whatever they wrote, and go with what's most LIKELY until we find out something different. The 9-bolt didn't use that ratio (41:12); it had a 3.45 (38:11). Neither of the people who have Dana 44s for this car are "likely" to be selling em on Craigslist in your town with $hitty ad copy (not "impossible", just, "highly unlikely") so you can largely discount that option.

The other G codes might tell: the 10-bolt and 9-bolt ones are specific to those models.

 

Ok good to know ,it was out of a 92 Transam. At this point don't want to trade my 9 bolt for high mileage 10 bolt.

 

I'd keep the 9bolt too, upgrade the carrier and maybe axles if you have a bent one