Jugs had flush rivets for the most part, like almost all fighters in AH (buffs are a different matter). However, here and there they had some dome-heads, usually in areas of high curvature where countersinking didn't work well, or where the skin was too thin to countersink. There were also some blind fasteners, which stuck up like domeheads, in places where the sequence of assembly precluded getting to both ends of these fasteners at once. However, on the Jug, all these things were few enough to ignore. If you want to be truly anal, get a "Walk Around" book or something similar and scour the detail photos for them. But they're pretty few and far between.
On this subject, I'm surprised nobody's mentioned the rather high percentage of domehead rivets on spit fuselages. On many of them, the longitudinal lines on the fuselage, especially aft of the cockpit, were domeheads, and on almost all of them, the row along the vertical panel line in line with the rear edge of the sliding canopy were also domeheads. They swapped out rivets many times on 1 of the 1st spits built to see what they could get away with without sacrificing performance, and found that the horizontal lines didn't make any noticeable difference if they were domeheads. Hence, they were able to save a fair amount of construction time by eliminating the need to countersink a lot of holes, and then inspect for flushness after installation.
