Is the socket bi-pin or PR? Assuming PR since you want to go with the ROP bulb.
The only option for the ROP in 3D size is Fivemega's 12AA/3D serial/parallel adapter, its 7.2V to work with the ROP bulbs. If the 12AA won't fit you'd end up with dead space. For 6AA, or 2 Li-Ion all you need is 2D. I guess you could use a dummy cell, but I would prefer not to have wasted space, especially D size.
What about one of Fivemegas bi-pin sockets and a bi-pin bulb?
You could fill the tube with 3 D cell Li-Ions or the 9AA/3D without any boring and run some of the lower amperage bulbs from WA or Carley that would yield longer runtime.
Litho has the Carley CL-809 which would be ~380lm on three Li-Ion. 9AA would be running close to spec, but still over 300lm.
Haven't tried it, but looks like the WA1171 would be ~450lm on 9AA.
For something higher, the WA1331 on 9AA would be ~650lm. Not sure about the host handling the heat though.
If 12AA do fit, you could use Fivemega's 12AA and some of the 12V bulbs.
Or use the WA1191 for ~385lm on 11 cells.
-Michael
