You can reassign any internal driver to any physical pin via software. For example, if you need 8 injector outputs but only 4 ignition outputs, you remap the pin functions.
For a full Electronic Control Unit (ECU) design and pinout, documentation is generally split into hardware architecture (schematics and PCB layout) and wiring pinouts (terminal maps for vehicle integration). ECU Hardware Design Components ecu+design+pinout+full