Great stuff.
I've been working on a couple of 7548's this past few week. Both are Japanese home market 7548-7000's that came directly from Japan.
They have different sapphire crystal designs out of personal choice.
One is a 1981 model. The other dates to 1982. A year between them but two totally different case designs. One is a fat lug. The other, a thin lug. Different case back motif diameters and case back designs.