It's not a RG3120 and I'm not too sure what it is, but the fact that it has a second set of serial numbers more or less indicates that this was SUPPOSED to be a J-Custom that was eventually exported out of Japan and branded as a Prestige. That also explains why you can't see any
strap buttons as some of the older J-Customs actually had the strap locks recessed into the body.
Seeing that it's most like an exported, prestige branded J-Custom, it looks a lot like an RG1308. Can't tell exactly but the body looks like it might be Swamp Ash which would coincide with the RG1308 as it was a
Swamp Ash body as well(it came in Natrual, trans blue and trans red I think).
