Hi.... I have the exact same plane (my second one to be exact) but that is another story.I have the tank tucked into the front of the fuselage right behind the firewall. I am not to sure at this moment on the CG as I don't have my manual in front of me right now, but I can get you any info on it that you would like on Thursday night when I get back home. I also have the throttle servo installed into the compartment beneath the tank ( there should be a small hatch on the bottom front of the fuse).
Both mine are, and were,terriffic flying planes when balanced correctly....it will land as light as a feather.
I am flying both mine without the cowl on as I prefer the "Stick" look.

You can let me know if you want me to provide some info

Cheers
Curt