Hi! and welcome.
the MC16 and 18 are not the same. a lot of 18/21 bits can be swopped over to fit the 16 though. 16 bits are getting hard to find now, but most parts can be found second hand.
the year of the bike on the log book is not always correct. one of my 16,s is a 1987 the other a 1991. if its got a speedo cable on the front wheel is a 16 if its off the front sprocket its an 18. hope that helps.