I have several 35HP OMCs and run 13 inch porps on my 35’s with a couple of 14′ aluminum boats weighing approx 230 pounds (without the motor), so I think the 12 inch will be ideal for your 600 pound boat. Your Glen-L boat looks great! Nice job!
Dave
Here is my 1959 35 HP Lark on my 1957 Crestliner (13 inch prop):
