disconnect switch amp rating

I have a 66 Dart that I plan on racing a few times a year. Nothing serious but will be needing a disconnect switch since I will be moving the battery into the trunk. I see that there are disconect switches ranging anywhere from 20 amps to 300 amps. How do I know which one I should be using and what regulates me to those amps? I plan on using a 2 post switch. I plan on placing an order this weekend for some parts and will be getting an NHRA rule book included in this order so I dont know what factors into this.
Thanks
Rodney