wrote:
OK - got some more info.

The center of mass is something like 34 inches behind the firewall
and roughly 7 inches above the top engine mount point on the firewall.
so roughly speeking 13 inches above the prop centerline.

What is that the center of mass of, exactly? The empty airframe only (i.e.
no engine)? Or is it the center of mass of a complete airplane (sans fuel,
pilot, passenger, and baggage) with the engine mounted at the original
point?

I'm also curious as to how you determined the location in two dimensions. I
can think of a few ways of determining it, but they all involve a bunch of
effort.