According to my old Holley manual, it shows they made the Holley 06H LZ carbs with both three bolt and four bolt bases. They both have 1" venturi's , which is only slightly larger than an old Holley 94. I would guess the 06H Holley carb is maybe 200 CFM or so. The Lincoln Zephyr V-12's were small displacement engines for the number of cylinders they have.
I have no idea if they have a vacuum port for the distributor on th Merc engine you have. Or if the vacuum signal is correct for the factory Loadomatic distributor in the Merc engine.
Sal