I think I found it. Its slightly to the left on the right side. In the middle is the fuel filters and lift pump. there was a little thing sticking out with a screw on cap so that must be it.Howdy elyKtneguN, welcome to the tractor forum.
On a David Brown 990, which hopefully is similar to an 880, the tachometer drive location is in the center of the right side of the engine. It may be capped off and painted over making it difficult to recognize.