What do I have here???

[Turkslay]

I recently purchased a 1971 wingmaster 870 12ga. I thought at first it was the unicorn mk1 from the pics. It has the mk1 adapter, its parkerized and has plain wood stock. The forend has been replaced with a vintage pachmyr. Once I purchased I realized it had a 20" barrel instead of 21" and a plus 2 mag extension instead of plus 3. It does have the rear rifle sight like the mk1 on the barrel and is in the same serial number block as the mk1. It also has a number hand inscribed under the receiver DC90009. Sorry for being long winded I just have no clue if is possible its an old military shotgun or what I have. Thank you for input.

[Turkslay]

I can not figure out how to post pictures Im sorry. I will figure it out soon.

[Germansheperd]

Get us some pics

[Turkslay]

heres the pics hopefully

[Turkslay]

Last one with the dc90009 engraved

[tinka]

a good thing

[capnor]

I see DC 9000? Last photo.

[Germansheperd]

To answer the question: What do I have here? The answer honestly a FRANKENGUN. Although the bayonet lug/sling adapter is cool.
As far as the inscription underneath most likely a rack number from some agency/dept.