After days of trying, managed to extract the form from the part...
The winning method was to cut some of the edge off with the multitool, drill a hole through the form, support the form on a 1/4" steel rod supported on blocks, and belt off the part with a hammer and cold chisel. Very aeronautical, I feel like an Aeroflot mechanic.
I mark the centerline of the part, hot glue on a steel bracket for a level, and rough out a hole for the main landing gear strut.
Offer it up, and start trimming the edge agains the tyre. Make a ghost picture to see how close I am getting to the caliper and other hardware.