You might be just fine the way you are, Karl sure makes nice headers.
I have never run a can on this engine, if it is a tuned type can and you are too short you will see a definite decrease in power and a rise in temps. If it is too long you just don't see the power, but she runs cool.
You should hit around the 7's for the average 23x8 prop (nx, menz) and 7300 for a vess23a. That is what I got with a stock muffler if memory serves. BUT,,,, at your weight, you will be ballistic with any set up