Hoping someone may have some insight as to the differences between 590, 600, and 620 cylinders. I know the 600 cylinders aren’t available anymore. Reason I’m asking is my 600 has a small defect in the cylinder and I’d like to put a new top end on it. Runs pretty good but knowing it’s there bothers me. Considering the 590 and 620 cylinders are my only two options the obvious choice would be the 620. Having said that I’d like to know what the differences are between the three.