This may have been mentioned somewhere is this long thread, I'm still working my way through it, but the Stakeout Squad used cut down M1 Carbines as well as shotguns.
Mentioned short OAL mattered for some of their Stakeout Hide positions, Rhett's Cheek weld stuff strongly reminds me of several things mentioned in the Cirillo books.
Both Cirillo's book and Paul Kirchner's book on Cirillo very worth reading and taking notes/lessons from.
Also one of the few sources of incidences that required more than 1 or 2 solid hits from 12 gauge to end fight.
They also mention chronographing cutdown shotguns.