christmass tree (rite pic) was the (popular for p-38) rack system before zero-length racks appeared (left pic). btw, left pic illustrates not so popular 14*hvar zero-length rack mounting for p-38(L?), after which christmass trees invented. p.s.M8 4.5" rockets were launched from M10(M12, M15) launcher. hope it helps. in fact "p-38 with m10" is much more popular term in internet, and in my time i had a tough work to find out that rockets were M8, not M10.
P-38L was first with options: * 10 × 5 inch HVAR rockets on the outer hardpoints when the bombload was reduced to 1,000 lb * provisions for 4 × M10 triple launchers (also called Christmas Trees) for 4.5 inch rockets on the sides of the nacelles and on the outer hardpoints Check this out for M8 info: http://www.designation-systems.net/dusrm/app4/45in-rockets.html