your Model 12 is one of the holy grails
Amen.
A word of caution, there are Model 12 28-ga guns that were converted from 20-ga guns. True 28s are rare, and there are probably more conversions out there than you'd expect. Don't get too excited unless you're sure yours is an original 28-ga gun. Most converted 20/28s are fine shooters but they won't get the collector's price.