Yes, it can be done and mechanically, it isn't too difficult but the setup and measurement to keep it from making noise and possibly eating itself up is a fine art. I'd not recommend it if you haven't done one before. Also, without knowing what is in the rear, you might need a different posi/carrier since the 3.55 and the 4.11 don't use the same carrier unless the 4.11 gears were put in with a 3 series carrier with a spacer.
They do make a 4:11 thick gear,for a 3-series,so hopefully that is what you have. We need to identify which carrier you have first.
I guess your all assuming he has a CHEVY rear than? I think first you need to ID the rear. AS WE know there were 4.10 / 4.11 Richmond 12 bolt OLDS gears. Then you need a set of 3.42 or 3.90 to lessen the RPMs IF it is a Chevy could be a 4 series gear on a 4 series carrier. or it could be a 3 series carrier with a spacer (normally done more often than other stuff) or it could be a 3 series 4.10 (thick gear) on a 3 series carrier , or finally it could be a 2 series carrier with a ring gear spacer and 3 series 4.10 gears...lol... YOU NEVER KNOW.... So there are your options. Find out th e rear ID first ... than open the rear take some pictures see if you can get the eaton posi units casting if it is a CHEVY. We are all here anxiously waiting.... Jim Mitschke J D Race
