Early troffers like these
Daybrite units from 1941 were preheat. The 1x4 size was more common back then, probably because 1x1 tile ceilings were more common back then compared to 2x4 T bar ceilings. The troffers in that catalogue were all preheat and a 2x4 model was also made.
Early troffers were typically a lot deeper compared to modern troffers and had the ballast above the lamps. I've seen a 1x4 one before, it was from the 1950s and had a huge 25/60Hz ballast. The ballast was the size of a modern VHO one.
Converting a rapid start T12 troffer to use preheat is fairly straightforward. You'll need 2 modern (post 1950s) tulamp preheat ballasts which have the exact same mounting as a 2xF40 ballast. You'll need to get starter sockets and drill 4 holes in the ballast cover for the starters though.
BTW, preheat F40 ballasts were made in a 3 lamp lag-lead-lag configuration and 4 lamp series F40 rapid start ballasts were made at one point too. Those never really took off and most troffers continued to be fitted with 2 2 lamp ballasts until they stopped making new magnetic F40T12 troffers in around 2005 or so.
