Refreshing brakes - what should I look at?

Next time in there you can check the heel and toe of the linings for wear pattern.
Good tips in here under 1969 Drum Brakes
Master Technician Service Conference - Chrysler's Training for Mechanics

If the shoes are fairly fresh, make note of brand and any info for future ref. If you like them, get them again, if not you won't buy those again. The linings may have code on them. Primary and secondary shoes sometimes have different lining but that's less common to see these days.
Like these.
upload_2020-4-14_13-40-27.png
EE or FE is the friction code
Brake Lining Edge Codes

if you see a stamped number on the metal, thats the frame type. These are
upload_2020-4-14_13-42-15.png
Only used in 1968 as far as I know.

The rear ones on your car are probably 331.