Super Six Exhaust

I am running newly rebuilt 225 super six motor on my 71 Scamp. Currently I have an older exhaust system with 1 7/8 pipe throughout with a stock muffler. The motor s running hotter than normal and I have a new radiator , condenser, thermostat, fan shroud and seven blade fan on the car. I think it needs to breath more. Can anyone recommend and exhaust system/size pipe for a single exhaust pipe? I was thinking to go with a 2 in pipe and stock muffler. don`t want it to be too loud.