Hopefully either Marc R or Defendi will get me straight, since that would add another bit of errata to the design example. For the moment I'll go with the idea that the fixed mount is free as indicated in your post.
My Excel spreadsheet is modular in format, the top section, frozen in place, displays the data from the previous sheets or allows you to test different combinations without having to go through all the earlier steps. On the module page you set the main parameters ISC/Empire/Non-aligned, TL, Speed/Acceleration, Mass/Volume/Power/Cost/Crew, Type of vehicle, and CAT.
In the body you make the appropriate selections say for a disruptor that included changing TL, CAT material of the hard or strong point.
I copied the Ion cannon page with the entry with the mount parameters set for cost, which threw-off the cost calculation.
I've condensed the SM: P VM to 6 Excel portrait pages inserting the changes for the payload pallet hard point. After I'm done should I have someone like Marc R review the document? Where would I post the document, if approved?