They're not unusual to find on the hardtops, at the junction of the quarter panel and the lock pillar (door jamb) at the top.
I've also seen several bubbles/blisters at the top of the cowl on '68-'69 Bs near the A-pillar, that are apparently a reaction of lead filler under the paint.
There was also a problem with the rear shock crossmembers tearing away from the trunk floors on some cars, had a '68 like that.