I'm into this swap right now actually. It's not a bad transplant. I put a CH18S from a 2185 into a 682 (kind of). It's a 1641 frame I'm using with some other stuff, but it's the same frame as the 682. You do need to make some wiring changes to account for the differences in ignition systems. You will also need to drill new holes in the mounting plate for your 682 to mount the engine, or you could get one from a cyclops tractor and mount it right up. You'll have to modify the driveshaft also. Here's my thread on it, but again, I'm doing more than just an engine swap.
http://www.onlycubcadets.net/forum/s...ad.php?t=49314