Mike,
Looking at the upside down Hi-sider in NG Pictorial Vol-3 pg90 there was a union/break in the Brakepipe some 2-3ft in from the headstock alongside the draftgear casting, and I note the D&RGW had the Anglecock secured by bracket attached to the Coupler striker casting, which unlike our rolling stock, put the Anglecock aways out from the Headstock.
I'd suppose that the draftgear was removed when converted to the plowgon which would then leave the Brakepipe unsupported. I wonder if the Brakepipe was then shortened back to that union point and blinded off. There would certainly have been a lot more work to reduce back to and then rearrange the pipe directly to the Brake cylinder.
Was there an AFE regarding the rebuild in the twenties?