Maybe I should have started with Where did I read the way to be able to get a good C/G reading on a new construction (as in with fuse only) so that I'd have a good ball park setting.
Any suggestions???
Start by looking at similar size/performance planes. Adjust for the weight of the engine(sticking an LA 46 in a Nobler will make quite a difference compared to an unmuffled Fox 35). Increasing the size of the stab to 22-25% of the wing will allow a more rearward CG, using Fancher's rule of thumb.
Best bet, especially if it is something a bit different, is to design if from scratch, using Wild Bill Netzeband's articles, some weights from other planes for the stab, rudder, weight of finish/sq.in., landing gear, etc. and do a weight and balance ala' Tim's suggestion above. Plan on the first one being a prototype, at least until you get it to the point where you can tape and pin everything together and see how close it is coming to what you figured. If something is out of whack, you can still add or hack where needed to get really close.
The last one I did like this from scratch flew right off the board. The only mistake was that a 3 in. bellcrank couldn't handle 3 in. wide elevators in anything but dead calm weather. I hadn't done WB's calculations for the forces on the pushrod(my bad). Putting in a 4 in. bellcrank, a longer horn, and building a longer span stab with the elevators narrowed to 2 in. wide pretty much fixed everything.