It would seem that yours could be turned into a 8 ga. and still have plenty of "meat" left.
The most important measurement is the distance from the rim to the extended rib. The extended rib was the same dimension on all guns, and the distance from the rim to that rib is crucial as seen in the picture. Your gun, with those measurements, I would think falls into it as being do-able.
I don't have the specs either for an 8 ga, but I'm sure someone out there does and will post them.
The late Russ Ruppel had some of your information down as to serial number, barrel length, Quality 2, he also had uncheckered? next to it.
I picked up on the serial numbers after he passed. I believe he had 40+ in hammerless and around 20 in hammer gun.