426miller,
Just to give you my setup, it works very well, at least for me

I'm using the Greve pipe and a dual plug head. A5 as center plug and OS-F as rear plug. The total length og my pipe setup is, measured from the middle plug and to the end chamber of the Greve pipe: 87 cm. I have added 2 extra head shims (total of 3). I use a APC 18x10 propeller and 15/15 nitro/oil fuel. The 18x10 propeller accelereates my plane very well with this setup, and I have to be quite restrictive on using full throttle when flying the Nordic sceadule.
Regards,
Dag Ragnar