The older lifters had one gauge larger bores to accommodate the interior dimensions of extruded brass shotgun shell. In a 12 gauge you will typically find bores to be .751 or 11 gauge rather than the standard today of .729. A rough guess at constriction is to measure the muzzle with calipers and subtract from .751. Roughly improved cylinder would be .741, modified .731, full .721, and extra full .711. You can pattern your gun at 10 yards and the results will be: Cylinder 19 inch circle, Improved cylinder 15 inch circle, modified 12 inch circle, and full a 9 inch circle.
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