I'm in the middle of doing some ballast swapping to free up a 400 watt MV ballast and lamp for my (eventual) next refurb. I took the 150 watt HPS ballast out of my Lumec post top and converted that to Mogul incandsecent with a 500 watt PS-35 lamp in it. The big brother to this (4th generation OV 25) will get the 250 watt HPS ballast I had in this one. One remarkable thing about the ballast I'm using now, the starter components are integrated into the ballast itself so wiring is much easier.

Once the ignitor goes in the ballast though, the ballast will be junk though unless there's a way the wire and external one....

Ignitors are very rarely replaced anyways, most of the time a fixture that won't start the lamp will get a new ballast kit.