The parts lists I have clearly show well hidden breather pipe and 'P' clip;
‘Late A10’ Part #'s Breather Pipe 67-09222
'P' Clip 67-0923
Also in the '49-'53 & '54-57 books for Plungers, S/A Road Rockets and SS
Pipe shown as straight- bend to suit.....
..... the'P' clip attaches via a set-screw (#1-4606) to the underside of the Chaincase above the drive sprocket to act as a primitive and probably highly ineffective 'chain-oiler'