Hi, here are some of the issues. Older carbs, spacer and manifolds had smaller bolt patterns and bore openings. Yes if you are using the hot water adapter (if it fits your new carb) you can use the new carb gasket as a template to see how much comes off the adapter. you will want it to funnel into a cone shape and when the throttle fully opens you should be good. By the way many guys do not run the hot water through the adapter, they just by pass it. On my last post I didn't realize you are planning to use the adapter, I forgot about them and figured you are going to hog out the head the way I did on mine. Good luck