A friend presents me with an assortment of rivets and a shrug of his
shoulders, so I'm attempting to determine what I have.

An examination of Table 7-10 of the AC shows head silhouettes; not
diameters, just shapes. Most of these rivets appear to have the
universal head shape (MS20470), but come in different head diameters;
for example here one with a .15 diameter, another with .185 diameter.
so there appears to be something missing in the description - head
diameter. Spruce sells AN470 with a .250 diameter head.

Does anyone know how head diameter is taken into account? If I knew,
I'd know what rivet set to look for.

Taking the example from another direction, I have a rivet set marked
"T101E1-12" . GOOGLING got me no where. I could measure the detent in
the rivet set and imply a rivet head diameter, but without knowing how
head diameter is taken into account, I can't order a rivet set. Anyone
know how to cross reference rivet head size to a rivet set? - Mike