What D26 drop-in do you use with just one CR123?

Primaries, not RCR123.

I'm assembling a Surefire Lego 3P (LU60 + A21) and trying to figure out what drop-in to use with it. I do not want to buy RCR123s so that limits what I can use, somewhat. I also prefer multi-mode lights but don't want SOS, strobe, or any such nonsense unless it's hidden. I'd hate to take a Dremel to a QMiNi to steal its driver, but, if I have to...

I know that there are issues with fitting an LED drop-in into an unmodified LU60 and I have bored mine out to better fit them. It will not, however, fit the Malkoff drop-in as I have milled it out as far as I dare and the diameter is still a bit smaller than it needs to be.

If/when I build a light like that I will be on the lookout for a used Malkoff M30 to put in it. If no such thing, an M31. (although an 'M32' will probably be the module of the day when that time comes)

While that would work in a Solarforce L2M or a real 3P, the Lego LU60 + A21 combo will not, as stated in my second paragraph above.