I am so glad I found this thread as I was wondering the exact same thing lol
I have a klr 650 Tengai 1986 not sure about the a1,a2,b1,b2 etc... though?
Any help please to identify which model would be a great help
You seem to have some odd info, but from the UK, it could be possible.
I'll suggest if it was produced in the late summer/autumn of Year 1986, it is probably actually a 1987 Model.
To the best of my knowledge all '84/'85/'86 models were called KLR600's. But Actual displacement, was only 564mL.
There should be a cast displacement mark on the lower LH side of the cylinder, camchain Tunnel. Just above the gasket line.
Some country or countries apparently did receive a 1989 "Tengai" KL650-B1.
But the US of A, received the KL650-B2 1990 model and the KL650-B3 1991 model. The USA did Not receive any -B1 1989's nor any of whatever may have been built for 1992 and later.
In the USA, the internet has several sites to "Check or Inspect or Search your VIN" It should be 'Stamped' into the steering neck of the frame, behind the headlight.