Jose!!! This is an absolutely phenomenal dirk!! and my Highland blood is raging with envy
I have been going through resources for hours and I feel confident this example is much as you have suggested, but I think more toward 1770s because of the wider 'haunches' in the beautifully Celtic knot baluster hilt. The metal studs are of this period to 1790s.
Whitelaw (1908 (1977), p.313) notes that after the Disarming Acts of 1746, following the tragedy at Culloden, proscribed Scots from owning weapons. However the dirk, with its utilitarian purposes was typically permitted, and often the now banned Scottish basket hilts were dismantled and blades repurposed into those for dirks.
This blade seems likely to be one of these blades as its profile seems contrary to most specifically for dirks, and the fuller at the forte resemble known Solingen backsword blade types.
Clearly this dirk is for an officer in a Scottish regiment of the third quarter 18th c.+ as suggested by the military motif, the gorget, sword, cannons and the RB 2 is of course likely a regimental unit. This may well be a heirloom blade mounted in military dress as noted. It would be exciting to imagine that the heirloom blade was in use at the time of Culloden.
The cannon do not suggest artillery ...perhaps the RB 2 could mean Rifle Battalion 2 or some such designation but those units seem much later.
The style of pommel and the mounts predate the familiar stone mounted dirk pommels which began around 1800. It is amazing to have the scabbard also! This is truly amazing Jose, congratulations!
Sources: "The Scottish Dirk" James D. Forman, 1991
"The Scottish Armoury" D. Caldwell, 1979
"Scottish Arms Makers" Charles Whitelaw, 1908 (1977)
" Scottish Swords & Dirks", John Wallace, 1970