If you are talking about the CAD body in this
http://www.jemsite.insomnia-vhosting...ic.php?t=13325 thread, then the dimensions are exactly as stated on the blueprint for the 1989 Jem because it was modeled direct from the blueprint using the measurements on it. I can't remember if the version available via that thread is the final draught but I know the finalised version I did is available on the Project Guitar website.
Depth or thickness is 44mm
Width is a total of 270mm at the widest point on each side (which is upper horn to centre line and lower horn to centre line)
If you can't find a copy of the Blueprint, email me and I'll send it to you. It will give you all the measurements you need!