My copy of the ASTM spec for avgas (D910) gives the max Tetraethyl Lead
(TEL) content in milliliters (ml), not grams. 100LL has 2 ml/gal max,
80 octane had 0.5 ml/gal max.

TEL is about 1.66 grams per milliliter, and TEL is about 55% lead by
weight. Multiply it out and there is about 128 grams or a little over
1/4 lb of lead in a 70 gallon tank of fuel.

I'd like to see the reference which suggests a lower TEL content for
100LL is typical.

I use Mogas almost exclusively