Well shooting a bow with a 25/26" draw and 43lbs I don't think he has enough KE for most mechanicals. There are a couple that would work, but a quality fixed blade head would be the best bet. Something like a magnus stinger, or one of the smaller fixed blade heads like the 75 grn muzzy( muzzy does not make a mechanical head) which he may already be using if your post is accurate. Other heads would be a wasp boss bullet, sonic, razorcap or other heads along these lines.