Opening to block behind my Melling oil pump

I was working on my slant yesterday getting the oil filter and sending unit on when I noticed an opening behind my oil pump that goes into the block....I can put my finger in there.

I checked the part number M66C and it shows it to be correct. The gasket looks correct as well.

Is there an issue using this style of oil pump or am I ok?

Should I pack some foam or something in there to keep debris out if it is OK?

Thanks in advance for the help.