When we moved to the city I decided to give away all my archery gear, including a fine little book by Saxton Pope on the rediscovery of the joys of making and using the longbow. I had a couple recurves and an old longbow which I never strung or shot. I never did own a crossbow, though I was always interested in them. I recall that the De Young museum in San Francisco had a nice example of a stonebow very similar to the one I'm working on now in Sketchup.
The illustrations and plans I'm working from are out of The Book of the Crossbow by Ralph Payne-Gallwey.