What is the difference between the 305 and 350's? Is it just the crank?

 

No, the cranks start off life the same. They are balanced slightly different depending upon whether they end up in a 305 or 350.

The basic difference is the diameter of the cylinder bore. The 305 is 3.736" stock, and the 350 is 4.000" stock. The castings are different because of the bore difference.

There are other detail differences such as combustion chamber size, valve size, etc., that varies even between 350's and 305's. But, the bore is the distinguishing difference.

 

Well that's whack but thanks for the info. I was hoping it was going to be as simple as switching cranks. Thanks.