G'day Alan,
I was sent this information a couple of years ago when I first wanted to shoot wooden arrows, by a very experienced TradGanger. I hope it helps.
1. Start at your draw weight, and jump to the next spine group (eg. you draw 40#, so jump to 45# of spine).
2. If shelf is cut to or past centre, add another 5# (if bow is not cut to or past centre, subtract 5#).
3. If using a low-stretch string material, add another 5# (if using Dacron, subtract 5#).
4. For every inch of arrow over 28", add another 5# (for every inch of arrow under 28", subtract 5#).
5. If using more than 145 grains up-front, add another 5#.
That should give you a starting point. This formula has worked well for me (I can do final tuning with point weight and / or building-out the strike plate). The arrows that I have arrived at from this calculation fly straight and bring down big animals (well, small ones too).
Cheers,
Ben