This is the exact resistor I used:
http://www.mouser.com/ProductDetail/...M0vXW2IQ%3d%3d
The set was working, and working well during the brief test. Before I went about this replacement, I had probably an hour or so on the set with the original seleniums in place.
With the second dropping resistor in place, I'd be operating at 18.5 ohms. The voltage with 18.5 ohms was right at 253V, which looks good to me, as the Sams says 255V.