Bullsi,
In that situation, I can understand going that high. I' m a flatlander so 40 feet up is way up there to me.

The most important thing is shot angle. As long as you' re not shooting a really steep downward angle, you can get both lungs.
Since you are shooting a fallaway, you can put plenty of helical on your fletchings. I think the max is usually 8 degrees and anything near that will work just fine. The degree of helical/offset isn' t as important as getting a correctly spined shaft. I prefer 4" feathers, but good vanes work also.
Good luck getting it set up.