Below are some photos of the crank from my Series 36. I do NOT know if this is the same as a Series 80. The length is 10″ from the center of the square hole to the end of the crank arm. The square hole is 3/4″ between the flats. The 10″ arm gives about 1 1/2″ of clearance to the slash apron covering the frame. The offset is 3″. I would think some measuring would tell you if this would work on your Series 80.
Greg should know better if the S 80 crank is different.