Thanks for the info i have done some measurements as best as i can with the heads on the motor and the springs are close to 1.562 o.d. looks as big as the seat base is cut? must be a older set of heads. They run ok but i still am in question about swapping them over to a set of 310 cnc aluminums not sure of any performance upgrades other tham weight savings? I really dont want to spend that kind of money to go the same e.t. I could probably buy a glass front for what the 310's are gonna cost.and drop more nose weight.