If you go the Edelbrock intake and carb route, go for the 500 cfm - anything bigger on a 289, no matter how hot the cam, is going to be too much carb and you will be running constant rich mixture condtions.
Now do you want stoplight to stoplight acceleration, or WOT throttle power? If you go with headers, then you risk losing low end torque, but the stock exhaust manifolds are way too restrictive for any good power output, so consider getting the Hi-Po exhaust manifolds - looks stock, performs well.
You don't want to go over 10:1 compression, because if you do, you run the risk of having too much compression for pump gas.
If the engine is in decent shape and not in need of a rebuild, then get a Summit Racing catalog - they have everything that you need. For about 1K you can get the intake, carb, cam (and get new lifters), decent exhaust manifolds and spend the 80 bucks for a Pertronix ignitor - dump the points and condenser; no need to go radical with the ignition - the stock distribitor is adequate if the vacuum advance is operational. Don't forget little things like a new distribitor cap and good quality spark plugs and wires.
The major hurdle that you have are the heads - if they have not been worked on, then chances are you have heads that are designed to burn leaded gas - unlead gas burns hotter and will eventually burn the valve seats. If this happens, just take the head to a good shop and have hardened valve seats in while the valves are being ground. Of course you can find a set of 302 heads that are made for unleaded gas and have larger valves; larger valves = better air circulation = more power.
See how complicated this can get in just a few sentences? Don't give up, ask around - if there is a classic auto club in your town, join up and pick the brains of the members. Learn from their mistakes (and when working on cars, this can be costly - been there, done that, got the T-shirt)