I'd almost have to see it. Doesn't sound good from here. The 750 carbs probably won't fit into the 600 intake boots at all. Measure the oustide diameter of the carb throats where they would go into the intakes and measure the inside diameter of the intake boots, a tape measure will kinda work but a dial caliper would be better. The intake boots should be slightly smaller inside than the carbs outside. Even if ya do get the carbs to fit you'll really have to lean out the 750 spec carbs for the 600 or it will run way rich.