I have such a plan, it's for a A6M2 Model 11 & 21. It has a 78" span, but the plans could be made whatever size you want. The float plan is all on one sheet, shows all formers to carve a float out of foam. Shows fuselage mods and wingtip floats. I want to convert a Royal Zero using these plans so I am going to make a trip to the print shop anyway. I won't scale them to the size you want but I will make you a copy.

Dion