Yes, very rare. Many blew up in racing. They have ball bearings for the pinion and drive shafts through the cases, same as KR. And the same as KR/XR 750 ball bearing on both sides of the timing chest. Some engines have a tach drive in the distributor hole. Smiths tach was original. See if the numbers on the bottoms of the two case halves match, if not, one was replaced. The XLR & early Iron XR heads have a spark plug boss that is cast taller than stock Sportster requiring long reach plugs. It should have the KR/XR quarter speed oil pump. It's the same engine cases as used in the Harley streamliner Cal Rayborn ran on the salt with 89-inch top end. Last one I built on NOS cases got the alloy XR bearings, with single row on the right side, though later alloy XRs use double row, a Johnny Goad invention copied by the factory after early failures of the r.h. case. Another point, the left case under the primary cover should have a casting number ending in 57 R, and the inside of the cam cover itself should have a casting number ending in 52 R.
