Mossberg 500AB help

[Hbibb1]

So I have an old Mossberg 500ab, serial number D90349. I assume it is a sort of special edition because it has the red recoil pad with white spacer as well as a jeweled bolt and lifter. Barrel is 28 inches with a fixed modified choke. Overall it's in pretty good condition given the age (estimated around early 70s), the stock has darkened and the bore has some pitting along with the outside of the barrel. Recoil pad is still somewhat soft but has signs of hardening in places. My questions are can a mag extension be added to this old style tube? And I would prefer an 18" Barrel, would you recommend going ahead and cutting it down given it's less than ideal condition? I would like to shorten the barrel and throw on an old school heat shield to give it that trench gun look that I feel goes well with the original stock and I think a shiny new barrel would look out of place on such an old gun. Any thoughts, input, or info is much appreciated.

 

[Old Shooter]

As far as the barrel goes, check the pawn shops and gun shops to see if they have an old take-off barrel. I've gotten a few for $50 - $75 in the past. Sportsman's Warehouse has the Matte finish barrels in 18 1/2" for $99. Does it have the vent rib barrel? There are several threads on here about how to deal with cutting that down. The AB indicates that it is a gun that was made for sale in discount stores such as Montgomery Wards and others, (that according to a web search). It is the same as the 500A and all parts should interchange. have fun!