Unless you want that thing to rust away to nothing I would flip it over... That fixture is going to fill up with water and rust out everything metal inside. That's what happened to my OV-15 TuDor and it needs a lot of work. Of course it's a labor of love but if you can save the fixture from needing all those repairs it's worth it. BTW, I painted the slipfitter bolts, slipfitter brackets, ballast core, and ballast brackets with black gloss enamel paint since they're rusty and now they're lookin' sharp.

that's the shallow glass GE used so I think this light is from the mid-to-late 70s.

This thing sat upside down under a catalpa tree for as long as I could remember before being moved to here as a "display item". There's a little rust and lots of catalpa leaves in there I'm sure but everything looked workable and we get usually less than 12" a rain a year in that part of CA.
I wonder how buzzy this ballast would be and what the possibly-PCB-containing capacitor would do when powered up for the first time in decades...

Ah I see. Here just being outside alone is enough to rust bare steel things since it's so humid here and we get lots of rain.

Ballasts are unpredictable. From my experience, some GEs sound like hornets' nests while others are dead silent. The fewer coils, the quieter it should be. I wouldn't worry about the capacitor...

Same here...lots of rain! If this thing ever sees my off-grid house someday it might have to get the MSW inverter electricity test and see how noisy it is then!