As the title says, I need some guidance on the proper plumbing of this Remote oil filter head.
Item #1 part number 848555T.
Thank you for any help.

20 connects to 8 and 28
21 connects to 9 and 25
18 and 19 go to the cooler 29 and return 30

I think ? someone else take a look

I'm seeing this,

OK, I'm using a Hardin Block adaptor and cooler so,
what you are saying is
#20 = OUT Block Adaptor and IN Filter Head (center of filter)
#21 = In Block Adaptor and OUT Filter head (side of filter)
#18/19 to oil fittings on cooler.
Is this correct?

Great, AllDodge, What has me a little confused is when I blow in the "IN" of the filter housing it directs the air to the cooler, shouldn't it divert it around the cooler to the filter (ambient room temperature)?, bypassing the cooler, or does it take oil pressure to activate the thermostat flow?
Also, what is the big plug #2 for?
and #16 Switch, Choke?

Using your pic (not mine)
I have not used one of these but my thoughts are, 2 is the thermostat and 16 is a low oil pressure switch.
My pic, 2 would be plug to install gauge
The switch would normally be installed on the block but could also be installed on the thermostat housing

I would suspect that the Stat would allow oil to flow freely until pressure builds, otherwise the cooler could be empty until it got hot enough, but just making a guess

https://www.mercruiserparts.com/bam/.../31323/2320/21

Regarding the plug I was referring to #7 (not #2 my eyes are getting old). Your picture is #2 but it is 1/2" x 14 plug
Thank you

the #'s on your chart and AD are different, I had the same connections but not colored lines

your 7 is thermostat