I can't speak as to using the ZDZ-80, but I can tell you that
with the tail level, I measured 13 1/2" from the centerline
of the spinner to the ground.

As for achieving the 5 3/8" C.G. Here is what I ended up doing.

I have a 2000mah receiver pack mounted about in the middle
of the lower wing. I changed the rudder servo setup to a 1/4
scale Futaba pull-pull cable system. I mounted this servo inside
the fuselage near the back of the lower wing area. That said,
I had to add 3 1/2 oz of lead to the tail section. I epoxied these
in the middle of the fuse throught the cutouts for the elevator
servos.

I didn't beef up the firewall at all. I mounted a B&B cup directly
to the firewall. So far it looks good.

I'll try and get some pictures of my setup posted soon.

Do what you have to do to get this one in the air.....you won't
be disappointed.