Pentagon PX-1 can use a Malkoff P7 P60 drop-in and M30 and pretty much any P60 drop-in. The PX-2 will need the M60, but it too is P60 compatible.
I used my PX-1 with a 6P tail cap and a P7 as a Lego. I just kept the springs from the stock incan lamp in it and wrapped the P7 with aluminum foil many times over and it worked flawless..
The Pentagon light with a 6P twistie was a pinch shorter than my real 3P. I still am trying to make the shortest possible 3P clone. So far I am at 3.54inches, but soon I hope to be 3.25inches with a 3P parts cropped and chopped.
There is my PX-1 on the far right with a 6P twistie and in that picture I beleive I had the M30 in it, but the little E1e had the P7.