Buy some black silicone, and use it instead of the end seals that come with the manifold gasket kit. Just don't use it on the gaskets that seal the ports! Gasoline will dissolve silicone and cause a massive vacuum leak. The reason for this is that the end seals usually don't seal that well. Be sure to use a healthy bead of it too. I like to use it without the plastic tip that comes with the tube of silicone. Also, get some brake parts cleaner to clean the mating surfaces before using the silicone. Otherwise, it won't stick. Another thing you want to do is be sure to clean the old gasket off the heads using a razor blade and/or 220 grit wet or dry sand paper. While doing this though, be sure to put an old T shirt in the valley and stuff the ports with paper towels so that the old gasket materials don't contaminate the engine. This also helps if you drop a nut or bolt while cleaning stuff. Likewise, until you are ready to bolt on the new carb, keep duct tape over the inlet of the manifold. This will keep bolts and washers from dropping down the manifold and going into the engine. I say this, sadly, from experience.
