One option is to add a compression "T". That way you can use the old gauge and a new one if you like. Same fittings as the "new" plastic line would use. Check with your local FLAPS.
The other option would be a compression union to mate the new gauge to the old line. Only one gauge that way. I hope that is helpful. FYI: that little tiny oil line will let a LOT of oil out real fast so make sure the connections don't leak.


Steve H