A couple of things...

Grade 8 hardware is a fully heat treated item. Much strength and mechanical properties will be lost from welding.

Single pass welds should be OK with S-6, due to the pickup of alloy when
welding (dilution).

Most of the Grade 8 I have come across is plated. Zinc, zinc-chromate and other platings are used often.

Wax is sometimes applied for consistant torque readings.

Good Luck

brande