I have one of those, No need to block off anything, The two pieces are bolted together. just unbolt the oiler section, The ports are all threaded so just screw fitting into the regulator,
I have one too, and I also removed the oiler section from it. I've got just the water separator and regulator, and the oiler bit is in a drawer somewhere. Of course it's possible that they changed the design over the years - it's from the Omega Wolf days, and before they went into administration some of their products were a bit variable as they tried to get them from different suppliers before finally giving up as Aldi were selling more than they could import. You could of course put a thread on it with a tap if it doesn't have one...