RE: Old C.G. location
On a plane that small - 1/2" is noticeable
Your "oldtimer" is nothing like I had envisioned .
To me an oldtimer is a 1950's tube radio setup -
Yours is a "multi" stunt job .especially one with retracts - which were at that time , pretty lame mechanical thingies.
assuming it has a straight rectangular wing - set the CG for 25%.