My only reference in inquiring: A skilled-sheetmetal-fabbing-friend was building himself an aluminum framed/skinned airplane. Low-wing - maybe sort of like a Beech Bonanza, sans the V-Tail. After a year or so, he got the wings and tail assembly done, started on the main fuselage, and he gave up for some reason (divorce, loss of interest, money, fear?) and sold the pieces to somebody. The riveting process was very laborious - the rivet holes had to be drilled, and lined up perfectly before the pop-rivets could be installed. (No spudding or reaming allowed). He had purchased dozens and dozens of Cleco fasteners to hold it all in place while riveting.
I doubt they would be all pop rivets, a skilled sheet metal worker can get a bucking bar into very tight spaces to compact the tails of the rivets, we had quite a few special bucking bars to get into tight spaces. The first skin of a repair like that would be all solid rivets, the second skin could have some pulled rivets in the tight spaces, but would only be a few.
But I was not there doing that repair with what materials they had at hand at the time, so my opinion is not meant to be the final authority on that repair. Just my 20 years of experinace doing simalure repairs. Cheers.