Jon, There are a lot of clubs that now allow the duplex carbs/manifolds on JD's in speed limit classes. My local club(MATPA)has allowed them for several years now. The heads bolt on an "A" without mods, and on a "G" if the head is from the all-fuel 70. One thing to remember is that with a speed limit class, the horn takes care policing power. It doesn't matter how you achieve the power under the hood as you can only go so fast.