NGK BR8ECM
i use only this plug in my 250, 360, 500 ... its easy handling and on the big engines it gives the right clearance to the tank..
nice bikes on the first look,
... its a little bad that the k5-engine is worn out, but new rod,piston crank bearings seals and plating and you´re back in business and it make sure, you have a great engine in the af-frame if you finish the projekt...
service honda use a light modyfied cr500 exhaust on their kx500af-bikes... you can buy a aftermarket cr500 pipe and weld the right kx500-flange on it for the cylinder-fitting . thats easier as cutting off and welding together the whole old k5-pipe ...