Thanks for the comments to all. I will try the acetone and/or paint thinner to see what comes out.

The bike is an old tandem Peugeot with a mixte rear and some interesting components like super champion competition rims, TA cyclotouriste cranks, lyotard pedals, etc. It had a respray at some point, and I started sanding just to see what brand the bike was. I considered preserving the small lion area decals on the seat tube with tape and having the rest blasted and powder coated. Still weighing options, but will likely just coat it all.