Interresting project
The header is critical when using tuned pipe. There are many pipes available on the market today: BMB, KS, AMT. If you go on BMB website, you can download some RPMs with different props/header lenght.
http://www.bmb-daempfer.de/daempfer_eng.htm
1) What prop do you plan to use?
2) Will you put all the pipe inside the fuse or let the pipe's tip going under the fuse?
I am running Mejzlick 26x10 at 6800 RPM on KS-95 can. I am sure you can turn the same prop over 7100-7200 RPM with good pipe but, if noise is an issue to your field, i would tune it for 6400-6500 with CF 27x10 prop.