Okay I've narrowed it down. My CB550 is either a '76 or a '77. Which year is it? The number on the motor is CB550E-1111343('76, according to this website). The chassis is CB550F-2002074 ('77, according to site). Something fishy going here. My first guess is things were switched at one time or another, judging by the wiring harness (looks pretty rough). Or did I just get a late engine with an early chassis?