Bob,
I used 3 hinges per side. Some really nice ones I picked up at the Woodcrafters Store. They were brass, unlike the original steel. But after a coat of paint the look just like the originals Stanley Trunk hinges.
Like you I was confused on the spars, as I could not find any good photo's of that area. So I went with hinges on top, and beveling the elevator spar.
When in doubt, remember, 99.9% of the people that will see the finished plane will think it is great. I'll ignore the other .1% unless they can show me their 100% perfect replica.
