I once made a 50 in paddle bow out of Cypress that pulled 26 inches. Backed it with rawhide and the limbs were 2.5 inches wide. Held up for quite while, but eventually failed in tension. Fun little bow though. If you've got enough width, I'd go for a flat bow, 70 inches long and two inches wide for 2/3 rds of the limb, tapering and thickening towards the tips. And I'd back it with linen.
That or a short sinew backed bow.
Gabe