Stages are just marketing terms, there are no fixed or set definitions... If you get a big cam, you might need stiffer valve springs, clearance the valve pockets in the piston, lightweight retainers, etc. Just to theoretically make it all work together physically, and then supporting mods like a different carb, exhaust, ported head and a high compression piston so that it will run well together.
If you're thinking in terms of stages, it might be best to start small and understand what you're doing first.
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