Oil sending unit

[Flyingthere]

I have a '78 124 spider and want to add a oil pressure gauge that I got with the sending unit from a '77. Currently I have a wet gauge that a PO added to the car. I need to know if the connection from the '77 will screw in where the big nut appears or if I have to come up with something else. Attached it the current set up, it looks like it is a 1/8" NPTM fitting with the compression fitting on the outlet. (I expect it to be metric) I wonder if that is a reducer that the fitting is screwed into and if the standard sending unit should thread into that hole that the reducer is in.

Please share if you can I really want to make the change.

Thanks in advance

[BEEK]

the factory oil pressure sending unit will screw directly into the oil filter housing without any adapters

[Flyingthere]

So from what I am understanding that nut closest to the block is an adapter and should come out without any real issue, would you agree with that?

Thanks.