I my humble opinion, why buy a 336? Unless there is some kind of nostalgic reason, the 336 is going to be same ownership costs as a 337. Except for maybe some unusual gear issue or something, but the engineered changes on the 337 over the 336 is worth that risk. Just my opinion.
Here are some threads that might help. Used the search feature of the forum
http://www.337skymaster.com/messages...highlight=C336
http://www.337skymaster.com/messages...highlight=C336
http://www.337skymaster.com/messages...ht=differences
http://www.337skymaster.com/messages...ht=differences
BTW, had my Skymaster at your airport a couple years ago, nice field.......