Who doesn't like a good challenge. Ok, assuming you need the 'systems' info in this json path, if you are creating a 'system' record to then have child module records, you could solve this a few different ways.
One way, assuming you first create the parent 'system' record, you could then call another pipeline to add the child record of the 'module' since you have the parent record ID you just created.
Create a callable pipeline and use the record ID of the parent, and the module details as the arguments to the call, something like:
createModuleForSystem(recIdPar, actId, code, manfName, [quantity])then use the built-in create record step, voila!