ARC LS first run had a two piece head and originally came with three twistie bodies. it's heatsink/board only fits first runs. several style boards were made. two is shown below.
Wayne Y was truly a pioneer and engineered the boards for the world's first production LED light.
ARC LS w/one piece head had many variants, but all used same style board. ARC LS1, LS2, LS3, LSL, LSH, LSH-P, LSL-P, LSH-FP, etc
there were many variants, but here's the three basic board styles.
there's no heatsinks currently available for ARC LS. I've made proto-types on my lathe. but no one has put them into production.
I posted threads on this long ago. sorry don't have links..
part of the problem is ARC's board design is very short. to duplicate OEM stack height almost requires a similar board/heatsink combo.
twistie tailcaps can be easily bored out to accept a slightly thicker heatsink assembly. TSP's spring already allows space.