Maximum Turning Capacity

I restore OLD, old, old outboards, the kind with cast flywheels and such, while I can turn the OD on my 1913 Evinrude, 9 inch OD, I can't do the same for a 1915 Waterman, 11 inch OD... this is on my 1947 Logan 10 inch model 820.
Being mechanical , I will make a platform that will permit me to turn a 12 inch wheel, maybe more once I get the details figured out, OR I will try to find a 14 inch Logan or similar lathe

Riser blocks aren't unusual to find on old flat-bed lathes but making the headstock riser on a V-bed is an expensive proposition. If your only need for more swing is turning the OD of flywheels (and presumably not many of those), your cheapest and easiest and probably quickest solution is to find just the headstock part of a Globe Milling Attachment (see photo). And a riser block for your tool post. It and the tool post riser would only take a few minutes to set up after you make a bed adapter for it. You will also need to make an arbor to mount a chuck of face plate to. The only problem is that the one that I had, and all that I have heard of, have a No. 9 B&S taper. Globe did offer an arbor with a threaded spindle nose but the brochure does not say what the threads are, and mine did not come with it. If you decide to look into it, I have the complete brochure that the photo below is out of.