I've been through something similar on my '96 E350. There are two different width shoes and drums, and it turns out two different drum offsets for the same shoe width, for the Dana 60 full float axle. Duallay or non-dually, different widths, different diameters, full float, semi-full float, more options than Baskin Robbins 31 flavors ice cream
I wound up having to ship a wrong pair of those heavy-ass drums back to Rock Auto, lost about 75% on the deal. Then payed 30% more to source them locally. I see you are on an island, so I can imagine you have even worse logistics problems. Keep after it, you'll get it.