just a though on the strange bump/funnel/stack thing. Recall that in this era machine frames were cast iron affairs, and casting iron with sand required making molds. mold makers were professionals and it was a bit of an art ( though they were not really that well paid ) but if you have a working and proven mold, no sense changing horses mid stream. Also and this is just speculation and rambling molds parted and everything cast had to be made with a 'draft" ( taper so that it would come free of the sand.... the funnel could also have been the remnants of incorporated into the "sprue" the hole that the molten metal was poured into. has the correct tapered shape and a simple facing operation to cut it off flat is much less labor intensive than trying to machine it down clear to the rounded contour of the arm.