Dave is it really '75-'79? Perhaps more of '77-'79? Reason why I think so is because of the NEMA tag and the grooved line on the door for the NEMA and I believe NEMA tags didn't come out until 1977? Right?
Funny thing......my 1980 one has a door without holes....or even the line.....but it has a tag!
Some GE fixtures as early as '75 had NEMA tags. I know a pocket of GE M400 split doors that were installed on a freeway in '76 and most of them had tags! 400w mercs.
Ah....here's an example! MV modern style posttop reported as a dayburner........Bad PC recep. Wiring found, needed new PC Socket, Giraffe had extra, but....(knife sliced) (giraffe laughing and called for new HPS bronze modern style posttop)
Funny thing......my 1980 one has a door without holes....or even the line.....but it has a tag!