To get the "full effect" and highest RPM, you have to switch out the stock P/S for a pipe timing P/S. These were stock on the ducted fan motors but not the outboards. Set pipe length at 9.5", and fine tune from there. Good luck.
Heat won't be a problem as long as you don't go excessively lean. If you have access to a BM 4 flow meter, 100 will be a good starting point, you will probably end up at around 110-115.
I can get you a measurement for the pipe length tonight. As these are custom hand made pipes, the ones I have vary slightly in volume/.
Are you using the standard K&B carb and K&B remote needle for that engine?
If so, set low speed mixture disk to full open/rich.
And begin with the needle at 3.5 turns out. Depending on variable with your specific setup you shouldn't need to go leaner than 3 turns out on the needle.
Below are a couple of pics as a guide for pupe length. Mine measures at 50mm from the header mount bolt to the first weld on the pipe. I am running a little more prop, and higher engine timing numbers, so this length should be a conservative starting point if your pipe is the same. Best to start a little longer and shorten the pipe as you go.