Hey Marv,
Some nice jigs there but I think they are a little limited in range of movement .
If there are a few grooves in the jaws and you clamp a piece of something in the jaws first.
Then tighten your clamps on the arms you can do the same thing by doing an aligned butt joint.
Also if you have enough you can hold a variety of parts at various angles to be able to join them.
As a picture is worth a thousand words ( well maybe 100 words with inflation
) here are a few of what I mean.
Cheers.
PS: Phil, expect to see a few photos if you build one or some.