Electrical charging issues

I have been having an issue with the charging system in my vehicle. I purchased this vehicle from a lady online super cheap as it was not running and sat for three years. It was her husband's! He had turned this into a drag car so everything was gutted it was all motor no accessories. I went through and cleaned out the tank, fuel lines, new plugs, wires, dizzy, coil, cap, etc. Etc. I hand turned the engine to get it pre lubed it fired right up no hesitation! I then noticed voltage dropping every time I rev it or put a load on it. Cool! I bought new battery and alternator. Fired it up and took it out. Noticed drop in voltage again. At idle there is no drop only under a load! Now mind you, car was gutted, wires mickey moused and engine is from another unknown vehicle! I bet you are saying "go ask the previous owner idiot!" Lol I totally would if he was alive! He died with all the secrets to this build he had going. Anyways. I have the car idling poorly. Voltage is at 12.6v now I'm going to perform the test of alt. Or battery so I disconnected - terminal on batt and woke up a beast. I have high idle volts are at 15.2 and climbing so I shut it off and here I am. I don't know jack about electrical. Somebody please help!