The Aimpoint 3000 was introduced in 1989, and the Aimpoint 5000 in 1991. Either one could be considered correct for a BHD-era build. The two models also look very similar.
ETA: Regarding mounts, although the MIL-STD-1913 rail was not standardized until 1995, the dovetail dimensions were developed in the early 80s and the ARMS #2 carry handle mount was introduced in 1984, with what we call today a Weaver rail interface (non-standardized cross slot spacing). The standardized cross slots that eventually became the Picatinny rail came about in the early 90s. You can buy new ARMS #2 mounts made to Picatinny rail specifications from many vendors. The early Weaver rail versions of the ARMS #2 mount also come up from time to time on the EE or GB. Pictures from the period also show other mounts of unknown make besides the ARMS #2.
ETA more: I recently purchased this Aimpoint 5000 with early ARMS #2 mount from a seller on another board. The Aimpoint 5000 has an optional tube extension that threads into the back of the sight, plus an optional polarizing filter that threads into the front and can be used to dim the view through the sight and make the dot more visible in extremely bright conditions. Below are some pictures of the sight with and without the accessories and a detail view of the mount. The seller indicated that he had purchased this mount and sight in the early 90s and had them sitting around rarely used since that time. It has a 3 MOA dot; be advised these were also produced with a 10 MOA dinner-plate sized dot as well.
Here is the
other side of the
scope if you care to look at it.
The Aimpoint 3000 can be distinguished, as in the picture below, by the small vertical flat section at the top of the central body of the scope, whereas the Aimpoint 5000 is rounded all the way to the top edge.
ETA still more: On NDS-C7B upper receiver. Rear sight not yet installed while I
make up my mind.