I used a bolt on neck from CB Gitty for my last two builds. The neck attaches to a plank that goes through the box. To get the neck back angle right, I had to create a slight bevel on the plank where the neck connects. This bevel had to be flat, square and the correct angle. Please see the attached file to see a simple setup to do this using a bench plane. Planing%20a%20neck%20bevel.pdf
Hi, now that's using the grey matter.
Now that is much easier than the jig I made for my router. Quick and easy I like it.
I usually use a through piece to bolt the neck to on my CBG's and if I need a back angle, I cut the through piece with my Miter Saw.
If you don't have a Miter Saw, Plane or any other way to cut it, Stewmac sell Degree Shims made of solid wood for neck pockets of solid body guitars for about $2 dollars a piece. You can get 1 degree or 3 degree shims. You would have to make adjustments to the through piece height or adjust at the bridge for the extra shim height.