The 4-71 has the advantage of instant boost at very low speed, which is good for big loads, it can turn slowly and still work. However, mileage will be bad because everything is working at any cruising speed. The 4-71 is also very high on power consumption, high charge temperature, and physically large.
For EFI I'd use a big ex-factory Eaton like a Ford M112. Less weight, lower power consumption, lower charge temp, up to perhaps 12-14 psi max.
Someone looking for "traditional" appearance, without the big expense of a rebuilt GMC ($2,500?) could just make an adapter plate to attach to the existing inlet duct alongside the late Lightning blower. Now rotate the Eaton 90° CW to narrow it and point the discharge to the 292 intake. The adapter is now down-draft, use it to mount your carb.
