Hey Mark,
The oops clamps work but have a limited screw length so are not the suitable for very thick blanks. On thick blanks you would use a helper block on the other end of the oops clamp.
The best clamping system is the vacuum table, because you have no clamps in the way that you could hit with your bit, but it is also the most expensive of all workholding systems. It however allows you to do things like this 
If you make solid-body guitar bodies and necks, you can use this two-side method described in this video. This avoids cutting into your vacuum table.
However they show a method without vacuum table, but with a wasteboard and indexing pins, the body and neck blanks are screwed into the wasteboard.