Getting started is easier than you think. Getting finished is the hard part. As Mike said are you prepared for more bad news when you get under the sole?
Here is what I would do...
1) make sure you have a good foundation under the hull. If it is sitting on a trailer that's good if you plan to keep it there. If not then you need it well supported before cutting the deck loose because you don't know how well the stringers are attached. You risk a warped hull if precautions are not taken.
2) Remove the engine, console, and hardware. A frames and hoists come in real handy about now.
3) Check cap and liner for viability. The cap is attached by the machine screws holding the rubrail. A '75 vintage rubrail is probably ready to be replaced. The liner includes the foredeck, sole and inside gunwales. The liner is glued along the top edge and to the stringers. All the core matterial in mine was shot (rotted, busted, chopped up by previous owners). If yours looks decent it may be worth pulling it out in one piece and replacing the core for the bottom. That's a long shot but worth the look. If the liner is shot then its time to pull out the circular saw, sawsall, etc. I did save the foredeck on mine, rebuilt it and re-installed it.
4) Once the liner is out, I can almost gauranty the flotation foam is soaked. Not only what you can see but also that in the trapazoid stringers. Get some garbage bags and start pulling.
5) The fuel tank is under the sole where the large hatch is. Unless someone before you knew what they were doing and replced to old one, yours is probably go severe crevice corrosion (check my photobucket account for pics of what that looks like). It will have two straps and flotation foam holding it down. Dig out the foam release the straps, lift out the tank ( a-frame and hoist, real handy).
6) Since the sole core is rotted the floor of the tank coffin will be rotted too. I grabbed one end and lifted the whole thing out leaving the tabbing on the stringers.
7) Now you can inspect the stringer to bottom connection. The integrity of that depends on how much pounding the hull took. You'll see delamination of the tabbing at this point.
Just checked my clock, gotta go. This should give you some ideas.
MD