cam selection
 

what is the most cam I can get away with using press-fit studs & stock springs? ('66 289 with stock heads)

You can't really tell what size cam to use with just the valves and springs. You really need to know what the flow on the carb is. If its a stock 2-barrell, you probly shouldn't do any higher than like a .350 or so lift or your carb won't be able to keep up. The only thing in your valve train that would make a difference is the pushrods. If you get up into the .450 to .500+ range you will need shorter pushrods and at least a 600 cfm four barrell.