Mt Al,
The original barrels would have been about the same diameter. The 8X57JRSx20 gauge barrels would be different diameter on one or both sides. The original wood would not fit the combination barrels, so at least new forearm wood would need to be added. We can't tell from the photo if they kept the original barrels, made completely new barrels, or re-lined the original barrels to 8X57JRSX20 ga. If they used the old barrels or made completely new barrels and trashed the original barrel tubes, they could have used the original forearm iron with new wood fitting the new barrels. If they kept the original barrels for use, they could have kept the complete forearm to use with it and made a completely new forearm for the combination barrels.
Mike
