[BobCl]

I have a couple of 504 magazines in their factory packaging if you're interested.

 

[BobCl]

These were plentiful not so long ago, but it looks like they're getting hard to find. My new ones are spoken for, and I'm going to keep the used ones for now.

From the pictures I've seen the 547 magazines were painted or coated black while the 504's were bare casting, but they're completely interchangeable.