From my own research on the web, having the same interest as you re Firebird dimensions, but not having one to examine:
"the middle section is 4 1/16 " wide and 1 1/2" thick.
The "step" off the face of the middle section to the "wings" is 5/64" while the "step" off the back is 7/64".
Now for surprise number two:
The "wings" have a thickness of 1 5/16" next to the center section but they both taper down to 1 3/32" at their sides.
The taper goes from center section out towards the side edges of the guitar only."
I also found a photo that confirms/demonstrates that taper.
Hope this helps.
I knew the wings were tapered, also, the taper is symmetrical front and back. Both the front and back of the wings are tapered equally.
I haven't seen Fletch on here in ages.......... but then again, I haven't been around much eitherFletch...what ever became of your Firebird project?
Dougie, are you sure that the front and back are equally tapered?