FOR SALE: Is there a quick and easy way to tell a 610 from an 820 ?

[Mark Loraine]

West Bend engine difference between the 610 and 820, like bore size and possibly a way to tell through the exhaust port with a pair of digital calipers?  I'm trying to avoid disassembly but will likely have to pull the head off.
So anyways, bore size is needed indeed.
Thank You,
Mark L./SWNY