A cheap, CG machine can be made for next to nothing. This will allow you to "trial place" your weight at your leisure. Just a couple new pencils, and some scrap 2X4 pieces, or ?. I also put those slip-on, tapered replacement erasers on the pencils.
I would also check lateral balance.......with the wing on. I know some will disagree and say this is not necessary with a trainer. I just feel it only takes a few minutes and only pennies to feel YOU have done all you can do to have it balanced. All wood is not the same in density. Therefore, a plane could have a lot of heavier wood on the same side as the muffler, thus compounding a possible balance problem. I made a couple "pedestal type" stands, (again of scrap wood), shim these stands so the wheels are about 1 inch from a surface. (your bench or table etc). Take off the prop and rest the crank on one....... and rest the tail on the other one. I have a "dull" nail protruding from the tail stand. I also cut a slot and put a razor blade in the "nose stand" for a
bearing point. I made this lateral balancer for my first trainer and have used it on the 7 planes since.
PS... I did make a new CG machine from 3/4 ply and aluminum arrow shafts. The design is much different..... it's kind of like the one in the catalogs. The maximum plane weight on this is about 12 lbs. The 4* 120 in my avatar had the arrowshafts flexing pretty good!! Good luck........lownslo