I have installed brake booster/master cyl 50-3360 which I beleive was used in late 70's thru 80's dodge trucks. I am trying to find correct fittings from master cyl to proportion valve. Does anyone know what size and type thread they are?

Likely to be 9/16-20 and 1/2-20. inverted flare fittings/straight thread. Measure across the side port openings with a 6" steel scale ruler to confirm. these are fine thread and if both openings are 1/2 then (2) 1/2-20 brass inverted flare fittings which will be for 3/16 brake lines

Rapidrobert, I do have 9/16-20 and 1/2-20 fittings. The 1/2 spins in freely wheras the 9/16 is tight feeling and I did not try to force it to thread. I was curious if it was straight thread or pipe.

Straight thread. clean the adapter and MC threads (easy) with a wire bristle brush then lube em & visual on the threads for any damage. the 9/16 adapter might be 18 threads instead of 20 like I first posted but its a brake line inverted flare adapter so it is the correct one. EDIT while we are at it measure the # of threads on the adapter with a 6" thin steel scale ruler or a thread pitch gauge if you have one. The # of thread "peaks" in an inch so we can be straight on that