My tape-on wheelweights seem to be the same as Sean's.
It looks like air-cooled tape-on would be an acceptable substitute for 20:1 alloy, and the price is right.
I didn't try annealing the tape-on slugs. I don't know if it age hardens or not, but it may. If I had to guess, I'd say it is alloyed with around 1/2% antimony and maybe a little arsenic. This was tested about 6 hours after casting.
[mrow] alloy [col] density (grain/in[sup]3)[/sup] [col]BHN
[row] air-cooled clip-on WW [col] 2794 [col] 12 - 14
[row] 20:1 [col] 2775 [col] 9
[row] air-cooled tape-on WW [col] 2841 [col] 9
[row] 30:1 [col] 2838 [col] 4
[row] pure lead [col] 2854 [col] 4