This method will work for any airplane and you dont have to find the MAC of anything.

What you need to know before hand, is the CG range in relation to your Datum. In the OP's post, the Datum was the tip of the spinner (or the wall), so ALL measurements need to be referenced from this point.

If your CG point is 4" aft of the Wing LE and the wing Le is 12" aft of your Datum, then the math you get from weighting each individual wheel and its arm (the distance from the datum to axle C/L) should come out to a final arm of 12" if your CG is perfect.

I have a spreadsheet i made up and plan to do a CG how-to video once i get another odd/large model done.