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Hi, I'm trying to fit a twin port head which is probably model 20 onto my 30's model 18. Ive noticed the valves stick out of the guide (top of guide) more on the model 18 head as they do on the twin port model 20. My question is do I need longer valves or shorter springs ? the model 18 rocker box fits, I'm just hoping that the rockers are in the right location. Any help on what valve spec or so would be great. Ive enclosed two pics. Thanks Dave
