I´m rebuilding a ´78 550 Four K. New to the bike will be a 4 into 1 exhaust along with 4 individual K&N air filters. What rejetting will be required with the improved air flow, etc.? Can the existing jets be drilled out? If so, would someone with experience suggest what number to use? Are jets from other year carburetors interchangeable with the unique appearing ´78? Thanks.