If you are married to the TQ I’d find a different intake manifold. Running an adapter is a guaranteed power killer and distribution nightmare.
If you want a good selection of .904 lobes, Howard’s has the most I’ve found. Like a couple of other cam grinders, getting them to use them is near impossible, especially if you tell them it’s a “street” car.
I think 3000 is the lowest stall you should use.
Select your gears and figure out what you CRUISE RPM will be and pick your cam based on that. 3.91’s and an OD still might not get you 20 MPG. If you are married to that number you need to rethink your gearing and cam timing.