You have a short somewhere in your wiring. You cam measure the amount (in amps) at the battery with a meter which will allow you to calculate how long it will take to drain the battery flat knowing the Amp/hour rating of the battery. Something is completing a circuit somewhere in the car. It could be due to corrosion or burnt points on a contact in some switch that is allowing current to flow when it shouldn't be.
Your options are a battery disconnect switch or to replace the wiring and switches (the easy way out). Or you can attempt to trace the source of the short by starting at the ignition switch (by measuring the Ohms the switch offers to Voltage), then pulling all of the fuses one by one to isolate the bad electrical circuit. Once you know the circuit with the short you pull every inch of wire looking for a bare wire or evidence of corrosion (a green trace of copper oxide) at a point of termination that could be bleeding off power.
Also check for simple drains, maybe a bad adjustment on the interior door jam light switch not allowing interior lights to go off, check same and harder to find if you have a trunk light, same for a hood light if you have one. Check also console lights if applicable and glove box light.
Thanks Big Dave! I believe I will start with the ignition switch. I initially swapped it out with a 65 impala switch. I also had to rewire it as well. Do you have a pic or 'color coded' diagram of the ignition switch wiring? I'm pretty sure I got it wired correctlly but I am sceptical of the gauge of the wiring I used.