Welcome to the forum ! I'm not familiar with an engine number starting with JEF so it's probably from one of many re-manufacturing companies back in the day. A truck engine would have started with a T,Dodge car with D,Plymouth car with a P,Chrysler with a C,and DeSoto with an S. Also some industrial engines with IND. You can measure the stroke of the engine by removing the little pipe plug on the head over the #6 cylinder and inserting a stiff wire in the hole and measuring the total travel of that wire. The stroke on a 218 is 4 3/8" and a 230 is 4 5/8".
Did you get that # from the flat boss just above the freeze plug shown in your photo?