Thanks for the help, and yes, I did come across that page too. I took some pictures of the problem at hand which explains it. Well the other 4 engines I have don't have that inlet, but I guess this dry clutch motor must have been out of a late model MC21 or MC28.

Images: http://imgur.com/a/fqza1

Also, I've just assumed that it's an MC21 engine. I don't recall the guy who sold me the stuff actually saying anything about it so I guess it could be an MC28 engine too. I'll hopefully get a chance to check engine numbers tomorrow. There is an MC28 oil pump for sale on eBay (coincidentally from the same guy who sold me the other one!) so I may buy that one too since it looks like the right one. And forgive me on the dirty engines, I'll hopefully be soda blasting them in a few weeks.