For cars that have sat along while, I always replace the fuel pump and water pump. Other work would include:
Change engine oil & filter, suggest using diesel engine oil because it has the extra zinc to help the flat tappet cams survive. Today's oils have very little zinc...pollution EPA stuff, and it is NOT good for older cars with flat tappet cams. Do some oil/zinc searches on this forum and there is a wealth of info & suggestions.
Drain and flush out the radiator & engine block, then new 50/50 antifreeze, maybe replace the thermostat & gasket.
Flush brake fluid, suction all the brake fluid out of the brake master cylinder and then refill & bleed all 4 brakes at the wheels. Use DOT 3 or 4, DO NOT use DOT 5.
Remove trany pan, drain all trany fluid out & drain torque convertor if it has a drain plug, then replace trany filter (accessible with trany pan removed), replace pan gasket, and refill. Then need to run engine till fully warmed up, slowly shift trany thru all gears and check fluid with engine running in neutral or park...I foreget which one.
The body shop work will be expensive, and the rust is always worse than we all think. So only dive into the body work when you have deep enough $$ pockets, and depending on how good a job you want be very careful choosing a body shop. So many of us (me included) have been taken by poor body shop/paint work.
The 72 340 was a lower compression engine. The engine cylinder heads will need hardened exhaust valve seats, which is somewhat costly. The hard valve seats are due to todays unleaded gas which beats the crap out of the exhaust seats. Compare cost of refurbishing your old cylinder heads with simply replacing them with new heads. Several are available, such as RHS, etc. The factory intake manifold is a very good piece, wont get much torque/power improvement there; if your going to go aluminum intake manifold look for an Edelbrock LD-340 intake. Keep your eyes open and find one for sale at a discount. They show up on this forum now and then.. Do some searches on this forum to get ideas. It all costs $$ anymore.
Sounds like you have a great car to start with. Good Luck!!!
