Did one of the original fittings have a little plastic extension on it, that fit inside the casting?
The two on the filter adapter had the plastic quick release connections, so I pulled the clips off, and the washer that’s formed onto the pipe, I cut off with an inch of pipe, with a hacksaw. Reamed it clean, flushed with gas, blew it out with air, slid a flare fittings over the 1/2” pipe ( tube). Removed the stock adapter fitting from the adapter casting, threaded a 3/8” NPT nipple in, and a adapter to that for the female flare fitting in the tube to thread into. I’ll post a picture in a new thread if I can. Had to cut down an open end wrench and grind the end down more narrow to get the female nuts to turn on.