[Arran]

Russ;
  The 199 substitute looks good, it doesn't even look out of place when compared to the early 199s with the evacuation tip on top. I will have to keep this in mind if I run into an early RCA dry cell set. I also see what you mean about the difference in pinout between the UV-199 and the UX-199; the UX has a standard pinout similar to a 01A, #26, or a #30, the UV-199 has the grid connected to pin 1, the filament connected to pin 2, and the plate connected to pin 3. If you wired the bayonet base to fit the pin-out of a UX-199 the 3V4 or 3S4 will become a flashbulb. Of the two tubes the 3S4  looks like it may be a better match as a substitute in terms of filament current, not that it matters on a battery eliminator, though the gain will still be higher then a 199.
Regards
Arran