[Mart]

I doubt that Ford were worried about compatibility with wires by that time. They had been out of production by a few years by then. It's a bit surprising that the wires will go over the 40 drums at all, considering there had been 4 years of wide 5s in the meantime.

The reason for the change may have been that the drums were easier to press out, being a shallower draw. possibly marginally less material, lighter weight (I haven't a clue really) but there must have been a benefit to the change, either financially or quality wise.

Mart.