Along the parking brake hang up possibility, the shoes could be mis-positioned on the equizer bar (the bar that's in between the shoes on the rear). The parking brake lever actuates against this bar to transfer the motion to the shoes. If they're mispositioned, it will make the brakes drag.
The only old drums that there really is any issue with machining is the old Buick aluminum drums. The steel inserts have a nasty habit of separating from the drum during the machining process. Your drums should be avle to be machined just fine, provided that they're within spec (11.060" max).
One more thing, most brake shops do not grind shoes anymore. With most modern cars and trucks using 4 wheel disk and the aftermarket manufacturing pre-fitted shoes, there's not much call fo it anymore. Plus there's the OSHA and EPA liabilities concerning the dust from the grinding operation. There's a possability that a shop that services over the road trucks that re-line the shoes themselves might still do it, though.
