Strulag, as I look at the photo on the left, I see a small area in the upper right corner between the muffler and the engine mount, which is probably what I would try for re-routing the throttle pushrod. That would run the pushrod along the side of the interior of the fuselage, and should clear the tank. You don't have to have an absolutely straight line from throttle arm to throttle servo; a bowed routing, if not too severe, will work OK.

I've had installations where I ended up plugging one firewall hole and drilling another, sometimes a third or fourth to get the routing right. I've seen installations where the pushrod was routed through the plastic engine mount itself--with a hole drilled through the plastic and continuing through the firewall.

No question, this can be a tricky part of putting a plane together. I have also used delman's trick of putting an offset bend in the pushrod wire so I can come out of the firewall in one line, and with two bends offset the routing to get around one obstacle or another. I had one ARF that was so poorly laid out I needed to put in a pivot arm to drive the pushrod through the only clear spaces available, offsetting the routing by an inch and a half or so. Sometimes you have to do some radical thinking to get these buggers to work right.