Can anyone tell me what the back side offset is on my Rally II wheels on my 1969 Firebird. They are 14x6 factory wheels with drum brakes all around. I've heard from people with Firebirds that its ether 4 inches or 4 1/4inches but I don’t know for sure and I would like to find out. Reason being is I might switch out my drum brakes to discs in the front and I want to be sure it will work with factory wheels with no clearance issues.

As well can anyone decode the codes beside the valve stem for me? They read as follows MI-9 6 26 JM