9" or 10" drums...?

As far as telling what is on it now, the spindles on 9" and 10" brakes look totally different. The 9" has a goose-neck that comes in from the front or back (forget), not centered like in the 10" spindle. The wheel bearings are also smaller in 9" hubs, so the dust shield will also be. If you have the drum exposes, they should all have the max ID stamped in them, like "10.030 in max" or such. The size designator is the ID of the drum.

9" drums actually do stop a car fine. I had those on my 69 Dart for decades and never had trouble stopping. Of course I never tail-gate and am smart enough not to rely on brakes going down mountain roads. For those who drive aggressively and/or stupidly, bigger brakes can help, though smart always wins in the end. There are many cars and motorcycles with big brakes at the bottom of ravines off the Angeles Crest Hwy. We sometimes find their bodies decades later.