The question is a little confusing to me, is this a 12 guage gun or is it one of the Browning reproductions of the Winchester Model 12. If the barrel is available it is usually a simple process to replace the barrel on most pump and semi-auto shotguns. If you are talking about a break open type shotgun (over & under, side by side, or single shot) that is usually a very expensive process.
Browning.com has sn data under customer service.
375-550 dollars, depending on overall condition of your shotgun.
Located on the barrel or receiver.
if the gauge and chamber length are the same
No
Between 90-150 dollars.
It will be marked on the barrel.
Need a detailed description
The "R" on an Ithaca 16 gauge shotgun Model 37R denotes that the shotgun has a ribbed barrel. The ribbed barrel provides added strength to the shotgun's structure and helps with aiming and shooting accuracy.
50-500 usd
If it is a Browning Superposed 12 gauge it was made in 1959.
1929, if that is the complete serial number. Any ventilated rib would not be original, but a solid rib would be. If all is right with the gun, up to $800.