I didn't know they had a rating for looking at the sun. My personal arc welding helmet is an oldie with a fixed glass and you have to use your other hand to hold it against your face when welding. I never did like snapping my head to lower the helmet. I've used it before when viewing solar eclipse.

Those gas welding goggles are usually light filtered like you said. I have a couple of pairs, my favorite are round wire framed (John Lennon style) with leather side shields.
I never thought of putting two filters together. I guess it's the same as stacking eyepiece filters when viewing through a telescope.

Wonder you could get some of those goggles they wore when looking directly at an atomic blast? You know those all white ones. :)
SteveS