I had a 1986 24 Offshore with an 80 gallon tank that my wife and I replaced over a long weekend a few years back. Assuming the installation was the same in 1984, this is my recomendation. Take pictures of the existing tank in place and measure all of the supports/bracing that you can reach. You may have to use a sawzall to cut some of the 2X4's if you can't get the screws out and that is the reason for the pictures and measurements. You will want to install all new bracing. Disconnect all the fuel lines but don't pull them completely out as you will want to use the old lines to "fish" the new lines through. Just get them out of the way enough to remove the old tank. Mine was a very tight fit coming out and going back in. Lifting straight up and tilting as little as possible was the only way to get it out.
My new tank came from Mattsons in Tampa. He does a nice job. Make sure you use the proper marine grade fuel lines. Fishing the large fuel fill line was accomplished by removing the screws on the top of the fuel fill cap and pushing up from the other end of the hose to expose the clamp underneath. Once you remove the clamp, you can attach the new fuel line to the old one with some #12 solid electrical wire. Make the connection so that the new and old fuel line butt up in line with each other and make your wire connections as low profile as possilble so they don't hang up while pulling through. New fuel sending unit of course and don't forget to ground the tank and fuel fitting. Check out your stringers while you have the tank out and clean up all the crud. Bottom line, if you don't feel comfortable with it, pay somebody to do it right. Hope this helps.
