There are no 1966 Scout 80s. The Scout 80 serial numbers ended at FC124894 (the "A" is immaterial... just an indication of GVW class within the IH stable) and production ended July 14, 1965 (the last roll tests anyway, the line probably stopped earlier) and 800 production ramped up, the early models still using the old style serial number that started with "FC". Scout 800s debuted in late '65 as '66 MY Scouts and picked up at the old style serial number at FC150001 (to differentiate them from the Scout 80) before transitioning to the 13 digit VINs on December 12, 1965, at G165001 but the first Scout was G165294 (with a six digit model prefix before the "G"). Not to be insulting, just trying to clarify, you are sure yours is an 800 and the serial number is FC151121A? If so, then the tag is mismarked as an 80. Stranger things have happened. Your finger is covering up the last of the number so being the anal-retentive Binder Bookie that I am, I seek clarification. FC151121A would fit as a very early production Scout 800 built in late July of 1965. If you are not sure what yours is, post a front 3/4 view of your Scout and a full view of the serial number tag.