Nice! Can't wait to see it! I wonder if GE ever made these for Mercury Vapor light bulbs. I've never seen one of these use Mercury Vapor light bulbs before.
I've never seen a MV version of this either, only M-400R2s. I'm sure they were made though. The M-400A2 was made in 400W MH but the M-400R2 never was. The first single door medium cobrahead from GE to take MH lamps was the new M-400/M-400A.
Hmm. I thought you has some pics of mercury vapor M400A2's on your street light gallery website. Maybe it was a M400R2.