It was never put in a car. The 470 is a franken engine that Merc devised. used there own aluminum block with Ford 429 cylinder head...
Auto parts store should be able to access the sierra marine catalog, unless they are really dumb... which is entirely possible. Places like NAPA usually can get sierra marine parts.
you should also be able fins it here on iboats although I find their search functions to be useless. I use these guys because their parts search function works really well
https://www.marineengine.com/parts/mercruiser-stern-drive/index.php
can type in your serial number and will take it right to the parts list.
If Merc used more than one distributor type on the 470 will need to be able to ID what distributor is on there