The MK0 carb elbow is an Aluminum casting. It is identical to the MK1 carb elbow except both bolt patterns are 1.813″ for the Tillotson HL134a carb. The MK1 JLO LK101L elbow has a 1.813″ bolt pattern for the same HL134a carb and a 44 mm pattern for the JLO engine. It only has provision for the pulse port at the bottom not top and bottom like every West Bend 820 carb elbow I have ever seen. The MK0 elbow has the pulse port drilled, the MK1 JLO elbow does not since the JLO is piston port scavenged not loop scavenged like the Benders.
The 1″ bore MK0 elbow is on the left, a 7/8″ bore MK2 elbow is in the middle and a new US820 1″ bore elbow is on the right in the top picture.
The MK0 elbow is taller and longer and does not require a spacer between the reed cage and elbow like the MK1 and MK2 elbows do.