Whats the difference between the K&B 3.5cc and the 3.5cc SS ( I think it's the SS, something like taht, one costs like 10-20 dollars more than the other what's the difference though?)
What's recommended?

The regular 3.5 is water cooled. The SS version has an air cooled head with a reconfigured cylinder head and a different exhaust system, the same one that they used to use on the old inboard motors that had an exhaust throttle.
Warning: If you buy a new one, take the motor completely apart. There has been reports of metal shavings inside that could easily blow up the motors.