Power steering "chatter"

Saginaw power steering pumps were in most Mopars ~1973 - 1981, thru Dodge Aspens and Plymouth Volares. The pump has a tall reservoir, not round like your pump. You need the mounting brackets too. I don't know much about brackets for a slant six. I did take a large bracket off a Volare slant that had a Sanden compressor and a Saginaw pump further out. Might have been after-market. I left the pump in the junkyard. Some after-market, like Bouichillon Performance, sell brackets for Mopar, but I don't recall if they have one for a slant.

BTW, "shim" means a thin washer or (flat sheet-metal) used to adjust spacing. As a verb, it means "make a position adjustment". Don't feel bad. Much of the lingo here is new to English speakers too, and is "Greek" to all new-comers. To elaborate, "Greek to me" is a U.S. expression for something new that you have no understanding about.