there is such a variation in black locust,, my experience may not be valid,,
29 inches of draw with some questionable issues, might be pushing it with the stiff handle,, 66 inch bow,,
putting a thin deer hide or goat surely won't hurt anything,, and might make the difference needed to keep it shooting,, even thin black locust can be bad to crystal when over strained, ,so you might consider reducing the draw a bit,, make the handle more shallow and that will help on that,,,
Pope and Young advocated rawhide backing,, I put a deer hide back on nearly all the bows I made professionally and felt it added to the durability of the bows back,, even helping to endure rough hunting conditions,, or the accidental overdraw,,
that being said I do love and respect the self bow non backed,,,so I am of the school of what is best for each stave,,and I am big on overbuilding on not straining to the max for a hunting bow expected to shoot for decades,,one thing for sure,, what ever approach you decide on ,, you will learn if it is working or not,,