Oil pressure gauge needs a tube to feed it oil from the engine's oil pressure port to operate..you'll have to either remove the stock sending unit,or put a tee fitting in the engine so it can be retained if desired (so the idiot light still will work),or just run the mechanical gauge alone..the location on the engine varies depending on the year and engine,most are located next to the firewall behind the distributor,your 350 will have it there--it kind of sucks to get at!..
The proper fittings can be had at just about any parts store or hardware store..
I prefer using copper 1/8" tubing,but nylon is what comes with most gauge kits..you can get brass adapters to allow the use of 3/16" brake tubing too if you prefer,if you use metal tubing,wind some spring coils in it to allow for flexing and vibration..compression fittings with ferrules and copper or nylon tube are the easiest way to plumb one up..
A volt meter needs a 12V hot wire and a ground wire to work---the hot wire should be fused and controlled by the ignition switch,so it wont be a drain on the battery while parked...there is usually several empty spots in the fuse box that only get powered when the key is on,use a test lamp to see that its only hot with the key "on" or "run" position..
I would say a water temp gauge is much more important than oil temparature,you can put the sending unit in the spot the stock sender went,it should be on the drivers side cylinder head ,right at the front,between the #1 spark plug and #3...
