You're asking too much of the wood with a design like that. You're probably asking too much of red oak, period. But if you managed a 73# bow, and there will be density variations within a wood species. I won’t say it’s impossible.
Jim Fetrow made a high weight longbow outof a army surplus pine tent pole, iirc. That was a hoot.
If going for a D bow, make it 1.5" wide. But you want a stiff-handled bow. In that case, I'd make the limbs a full 2" wide.
If it were me, I’d go for long D bow. I’d want every ounce of limb working.
How thick is your hickory backing? Too thick and it’ll overpower the red oak.
