Adding a conditional option or parent/child relationship to the pylonUI of transportPylonsComponent would offer a much more intuitive and in-depth pylon system,

Not to mention the ability to reduce complexity of some systems attempting to find their own solutions to this.

How it could work.

if Pylon1 = Missile Rack
Pylon a-d show options for different missiles else these comboboxes are hidden on the Pylon UI

a perhaps less (work) intensive option is to just make it conditional instead of a parent/child relationship.
If pylon1 has attachment x, show pylon y