Just got a P60 E head and tail to suit an E1B.
It took me ages to get my drop in just right. I couldn't get the head to close up fully, and when I tried the lens o-ring kept oozing out.
Stuffed around for ages and was going to leave it for another day. In the end I found a reflector that had a shorter lip on it and the head sealed up perfectly. It was quite frustrating there for a while.
The drop in has a programmable 8x7135 driver which I took 4 chips off to make it 1.5A on max for better run times, particularly on 16340. LED is a Nichia 219B sw45k D220.
Took some quick photos in the dark (trying not to bother anyone with my late night tinkering) in the garage.
I'm pretty happy with it in the end.