Hmm hickory no good for belly?
This is not really true, though not best, it is not bad.
Here it always 80%+ humidity maybe more. So this means around 14% moisture content year round.
I make two hickory bow with bamboo backing and both take no string follow.
85# and one 50#, they are quite short too at only 62" or so.
And no, I do not use heat box, I just heat treat before glue up and add maybe 1.5" reflex, they come out straight if you tiller carefully.
Strange thing though, when made wider they took more set, and trapping with very thin tapered backing is key.
Btw, I never make hickory selfbow before, but I suppose it is much easier because ability to tinker with even after tiller.
Unlike with backed bow, it can be dangerous if you try to heat treat again.