Are you talking about the brake backing plate? The hubs are different widths for 1941 ,due to right or left side speedo drive and 1940 is also different. The Virtual Indian web site people should have a better knowledge of.
Hi, should of said bearing sizes were different for early 41 up to FDO 340 and FDO 341 and later was larger be. , the '40 hub is narrower 6-5/8" wide. The backing plates ,'41'42 made for plunger rear, '40 all 45's,'37 to'39 for 45ss,'36 for 45ss and '36 that fits standard 45 and 74 and 4cyl. Go to the Jerry Greer site and go to order from catalog and put your year in and go to part number and click on to enlarge for specs.