For me, who has ruined many many locust staves, I'd say overbuilt is the way to go. However, Jawge and Dave(Snedecker) would probably disagree. Locust, even though it is the strongest North American hardwood in compression, it is brittle and therefore suceptable to fretting...at least for me.
Take it real slow and don't stress the wood at all. Exercise it well between sessions and good luck. My only successful locust bow is 68 1/2" long, 1 1/2" at the fades with a slight taper to about 8" from the tips where it is 1" wide. Then tapering to long narrow tip(holmsgaard style). This bow I named "Sweetness" as per Jawge's suggestion, who is so successful with locust. Pat