BTW, making the steps on opposite mold halves allows you to slip the two mold halves together at a better angle than dropping it straight down and hoping you are lined up.
Agreed, but it depends on what kind of alignment system you use. Some alignment pins will only allow a "straight down" assembly.
Also, an alternative method for making the molds for the lip (bonding ledge) is to just use a flat plate (e.g. 1/4" thick MDF, plywood or whatever) and cut it to shape, such that you are left with a 1/8 - 1/4" wide gap to the plug. Wax the plug and flange on the mold, and bolt the plate in place, and fill up the gap with epoxy/microballoons. A syringe is good for this. When the epoxy is cured, you can remove the plate, with the epoxy/microballoons now bonded to the plate. The epoxy will now have the same shape as the plug. Elongate the bolt holes as described in post #2, to allow the small mold to be located a small distance inside the edge of the fuselage mold. No laminating involved.
Magne