If there is even the slightest possibility of you wanting to get a slug barrel or change the present barrel for a different choke you need the serial number to be above 855,000 or begin with "37".
Guns with serial numbers that are lower have barrels that are fit to that particular receiver and will not interchange with guns with a serial number above 855,000. The lower numbered barrels will also have the receiver serial number stamped on the barrel. Newer barrels will not have a number stamped.
Guns that have serial numbers that begin with 37 will interchange barrels with other non-serial numbered barrels.
The new "Ithaca" gun co. will take your low numbered receiver and modify it to accept "newer" barrels. Last I knew the service was about $225.00. Keep in mind once the service is completed your old barrel will no longer fit and they'll be happy to sell you new barrels. Your old numbered barrel may be used as a tomato stake...
On a side note. Should you buy an older low numbered gun and a non-matching low numbered barrel there is a chance it could be fit by a competent gunsmith, a chance...
