Also note many FADEC units are not mounted on the engine. As electronic boxes, they don't need to be engine mounted and can be located on the airframe in an area away from heat and vibration and more accessible for troubleshooting/change.
The only fuel system components that do need to be engine mounted are the pump (driven via gearbox) and hydromechanical metering/shutoff unit (these days normally integrated into a single LRU).
LRU= Line Replaceable Unit by the way
BA77 if you do want to find out more the recommendation of the RR book is very good. If you don't want to buy it check the ISBN number and see if your local public library can lend it to you.