Shot of the 1963 M-400's Guts

See? 120/240V ballast just like my M-400 split door. So I think my M-400 split door's capacitor is the correct one for this light too. Originally this light had two capacitors though. Then in the 80s they went around and replaced all the capacitors with non-PCB ones. But then when these were all removed, the capacitors were all taken out of the lights when they're removed, as they still consider capacitors as hazardeous waste whether they're PCB-containing or not.