I use TadCustoms 3712, 3718, FM 1794 in various hosts. From E1E, E2E and FM 1794 (adapting original tailcap still in progress). Although haven't tried with SF bulbs...But any bulb in range 3-6V as per lightsaver instruction will work, even 7.4V bulbs would do.
Tad Customs lamps and sockets future-proofed incan E, though fit in socket they may not meet the shock specs of Surefire lamps, they are quite wonderful for all my flashlighting. My problem (maybe not uncommon) is finding enough Elite heads to fit another E socket. With Lightsaver softstart tailplant into C tails and the better availability of 6P hardware, Surefire still selling P60 lamps, my desire for a P60 incan increased. A bored 9P original will make it into my collection, I bet, so many cell configurations, versatile, but the incan pocket light is always a goal. I want to see 2 cell 1000lm incan, even if I can't yet see a use for it.
P60 incan is not future-proofed, even if incan dropins are not rare. If I can't acquire a FiveMega FM-D26, I hope to steal the idea for a one off for use with Tad lamps, for me Tad Customs lamps nail all sweet spots. I'm keeping my E's, and collecting more bodies (and invariably more complete E2e's) but I can't saturate my desire for incan with what I currently have available (due to deficit of incan E heads). The journey is very slow, but recognizing what I want next is quite a lot of fun.
My ideal incan light is a Tad Customs A3712 matched with a single 1200mAh KeepPower UH1835P, and what is around that is becoming less important to me, though I want a build that is reliable, durable, attractive, and tactile... and soft start saves lamps. There are 18mm single cell tubes, I think Solarforce has a P60 single cell 18mm tube, the 3P bored also of course... the point is I think I can find complete lights, and I'm not as sure about finding loose Elite heads.
When Mark introduces his E incan reflector heads at Lumens Factory, my P60 dreams may fade a little, but soft start in the Standard P tail is such a neat discovery, I must have a build that includes it.