You can swap incan lamp assemblies/led modules in any of the 'old-style empty bezel' 6P/9P/G2/G3/C2/C3/Z2/G2ZL (this list is not all-inclusive), as long as the voltage is appropriate for the light engine. Since the P60 lamp is actually being pushed hard at about 5.5 volts on non-rechargeable primary CR123a cells (because of 'voltage sag'), putting in 2x3.7volt RCR123a cells for a total of 7.4 volts would definitely fry a P60 or P61. However, you could put in a P90 (3-cell incan lamp assembly) in a 2-cell light of the type that you have mentioned, since it is intended for what turns out to be about 8.25 volts on primary cells, but the runtime is going to be fairly short. A better choice would be to run the P60 or P61 off of a quality AW 17670 cell, charged on a quality charger, such as the Pila IBC. Lumens factory also makes aftermarket lamp assemblies for almost any rechargeable lithium-ion combination you could come up with, sometimes giving better performance than the stock Surefire offerings.