Flying10uk,
Most of the Sten drums here are made just as you describe. There’s a little more to it. Internal spacers are added to convert the Sten mag section into single stack and a string of dummy rounds are added to the drum follower to push the rounds through the Sten mag section. The 72 round Suomi drums are most common. They are cheaper and more plentiful here than the PPsH drums. They are both surprisingly reliable. The downside is they are heavy and you have all that weight hanging on one side. The MFG 50 round drum for the Sig MPX and the double Uzi drum are much more user friendly.
My favorites are still the iconic Thompson drums. They just ooze nostalgia and they really shouldn’t be clean without a good brandy and Cuban cigar.