Interesting to see design change between these 1955 RD17s and the 1956 RD18s. Here are a couple of RD18 photos. One shows a new boss apparently with a small nozzle in the location of the drilled hole. The other shows just the cast boss with no drilling but there looks to be a new hole cast in below? Neither one shows the original drain plugged. Seems the design was still evolving.
