Rudy:

My guess on the aft cg limit? If you are already at 38% my guess is you've already passed it. But if it flies well at 38% it's obvious my guess is wrong. Just keep moving it back until it does what you want.

Are you including the ailerons in your measurement of the chord? If you are not then your 38% would be some distance forward of the point I would call 38%.

The airplane looks nice, bet it's enjoyable.

Bill.