You are on the right track especially if are going to run a higher octane like 102+ . The second plug burns off the excess on the down stroke and depending how your ignition is setup may give you a lot of extra go! I would start with Drag Specialties or JP cycles they have alot parts for Shovels in the hi pro section or try looking for a copy of Walnecks, it's the auto trader for classic bikes. I know there is at least one company that specializes in Shovels. Good luck and please let us know how it turns out!
Don't do it it's a waste of money! I did it to my big bore 78' and I don't see any differencs! I think I use more gas. I got it at the Shovel place in my home town and spent well over a grand when it was all said and done! Turbo charge the sucker or go nitrus it's the biggest bang for the buck!!!!