Mount the servos at the positions shown on the plan. How you do this is up to you. I mounted mine in a plastic JR servo tray which was in turn mounted on hardwood cross beams.

The switch harness, receiver and battery install forward of this in the empty space between the fuel tank and servos. I made up a couple of 3/16" spruce rails and a dual purpose 1/16" ply cover plate with my name and address details attached which covers them and seats positively between the spruce rails against the natural tension of the receiver/battery foam rubber confined in that space. You could also make up an islolation mount and mount them suspended on rubber bands. There are quite a few alternative ways to tackle this, but the suggested location is perfect.

This location pretty much coincides with the CofG, so no matter what you stick there, it won't alter the CofG significantly, only add weight. If your CofG however is further aft than desired, instead of adding weight to the nose, you can move the battery pack forward into space beneath the fuel tank. However the short arm of this point and relatively light weight of the battery pack won't effect much difference and introduces a problem of securing the battery so that it won't move around, plus makes it fiddlier to access, remove and refit. As you undoubtedly already appreciate, an 8oz tank is a squeeze in its bay once you buffer it with foam rubber, and a 10oz is as tighter than a fish's arse. I would suggest you will require a 10oz with an FX ....unless you enjoy flights of short duration or wish to demonstrate your proficiency at dead stick landings.