Is this my original engine?
 

I have a 1976 924, and had to rebuilt the whole vacuum, and Cis Injection system, first thing I noticed is I have a ecu and all the oxygen sensors ect- did the 76 have all these elctronics on them? Or did one of the previous owners swap out the engine? (The engine is also extremly clean with no corrosion)

Don't know much about the 924. CIS on VWs didn't start using the 02 sensor after 1980. Might also be related to whether the car originally had a cat or not (cat used? then probably necessitated using the lambda sensor).

Yes they do have an 02 sensor and a small ecu (ignition module) on the left fender behind the headlight.