After clumsily stitching together Lemonymous' mech and weapon bases together one too many times, I have assembled a comprehensive Lua recreation of the Rift Walkers with easily replaceable parts for everything a new custom squad could need.
(The weapons.lua is pretty barebones at the moment, I may be updating this with some more complete weapon templates later.)
Download here: https://github.com/Hederarch/ItB-Squad-Template