I've made a few sinew backed juniper bows and they worked out great. I've also seen some original juniper bows in the Smithsonian, some backed, and one or two that were self bows. Juniper works especially well if it's sinew backed. I wrote an article about juniper in the Dec/Jan '08 issue of Primitive Archer...don't know if you have that issue, but it should help ya.
I would suggest backing juniper with sinew as it is weak in tension and may hold up for a little while, but will probably fail after several hundred shots. Because juniper is so incredibly flexible, you can get away with a shorter bow and bend some recurves in it (to keep the string on). I'd say about 1 1/2" wide would be good for your 66" staves, then taper to narrower (but definitely thicker) tips. I made a juniper bow like that, but the tips were too thin and the tips bend too much, resulting in a whip tiller. It's sinew backed so I can't bend recurves in it, but I probably would have if I'd have known the tips were gonna bend so much.
Good luck with it. I think you'll definitely be surprised at how well it works for a bow. By the way, I used Western juniper from central Oregon, and you may have Rocky Mountain Juniper in your state.
