Are you ready to become even more confused??
I noticed that your receiver is not stamped with a ordnance acceptance wheel or a war eagle. This would be to the left of the serial no.
Does that mean your rifle was never accepted by the US?? I sure don't know. Take a look at my "Home Guard BAR" on page 2 and you will see what I mean.
So,----since Winchester was the leader in the BAR program, did they make extra receivers and pass them out to Marlin and Colt?? I don't know.
Did Marlin stamp "MA" on parts supplied by Winchester?? I don't know.
Does anyone here own a Marlin and can shed light on how Marlin parts are marked?? I don't know.
We certainly need a few experts here.
In any case it would appear that your rifle may have some non Winchester parts. Obviously a difficult thing to cope with.
Try to keep things in perspective. Think of how few people in the world own a Winchester BAR. Or better yet, how many people in the world don't own a Winchester BAR.
I must close now. I just discovered that my Colt BAR has a Winchester rear sight and I am having a really difficult time coping with it.