Can we have a picture showing the whole of the front of the drums please as that does look very much like a 2-piece drum to me.

Base models, GL, 1.3, 1.4 and cheapy 1.6 models had 1-piece drums, which were tapered to the edge and the "better" models had 2-piece drums.

It was all to do with the brake bias valves on the side of the engine bay. Small-drum models had a 70/30 bias split
Big-drum models had a 60/40 bias split.

Part numbers on each drum:
1-piece drum = 81AB 1113 AF
2-piece drum = 86AB 1126 AA
2-piece drum "RS" = V86AB 1126 AA
Van drum = 86AB 1126 AA

Also, on the inside of your drum, you have a part number on the flange part, the number should be one of the following:
2-piece drum = 83AB 1A034 AC (up to 1989)
2-piece drum = 83AB 1A034 AD (1989 onwards)
Van drum = 81AB 1A034 BC