It's actually not too hard. First, you want to make sure you use oxygen sensor safe sealant. I use Permatex Ultra Copper RTV. The main places to seal are the back plate, the carb throat and the HSN banjo fitting. Take your time when doing this. You want to make sure you use enough sealant, but not too much as you can get it in the carb or HSN. Remove the back plate by removing the screws. Place a thin film of RTV where the plate contacts the mounting area of the block. Then screw that back in place. Remove the carb and put a dab on the throat where it drops in the block. Screw that back in place making sure it's well seated. Just make sure there's no RTV in the carb itself.
The HSN is a bit more tricky. Remove the HSN fitting with a small wrench. Be very careful. It usually has fine threads and you don't want to cross-thread it. When you get it off, you also want to remove the banjo fitting. That's the round fitting where the fuel tube attaches. It's been a while so I'm not sure if that threads off or just slides off. You want to put RTV on the top and bottom surfaces of that. But you have to be very careful here not to get any in the fitting. If you do that will significantly alter fuel flow and can cause problems. Then put the fitting back on. Carefully thread the HSN assembly back into place. Tighten it gently and then let the whole thing cure as per instructions on the RTV. Should be good to go then.
