I took the profile from my ES-1GT kit using a form gauge (one of those tools with lots of sliding plastic sticks that follow a profile).
Used it length ways and then multiple cross ways. Modified the actual thickness by checking specs for the Gibson online.
A lot of careful hand planing to get the end to end profile and then hand sanded the profile constantly checking the templates.
About a day and a half but it is pretty close now.
I have not done anything this critical before but it was not too difficult - just take your time.
The actual top and bottom surfaces are plywood sheet so will bend to their own profile - the trick is to not introduce too much stress into the plywood or it will pop the glue joints.
As you can see in one of the pics, I have plenty of clamps available and I think about 20 will be used to clamp it all together!
Early days though....