Hi Keith,
You are trying to do account assignment at operation level.
SAP Library - Orders (CS-SE/PM-WOC-MO)
Hope you have the new tab on Operation Tab page "Account Assignment Tab"
Also to copy the project automatically to work order.
"This Customizing activity lets you define whether project numbers, which are maintained in the master data of maintenance objects, or investment program numbers, should be automatically transferred into the maintenance order or service order."
Plant Maintenance and Customer Service - Maintenance and Service Processing - Maintenance and Service Orders - Functions and Settings for Order Types - Define Transfer of Project or Investment Program
Do the config with respect to Order Type and maintain the WBS element in the Master data of the technical object.
So whenever you create a Maintenance order with that order, system will copy WBS element / Project automatically
Kindly let me know if this is your requirement.
Regards
Terence