I started with a sander, then went to the dremel and finally pulled out a wood file. After the dust settled, I think the firewall ring is getting close to the scale shape.
A whole bunch of material on the firewall ring needed to be removed.
You can see the firewall ring inside the cowl. Now the cowl is about 2/3 past the face of the ring.
Removing balsa and contouring the ring provides this gap between the cowl and the ring.
I didn't measure it yet, but I'd estimate the cowl has been moved back about 1/2".