According to the BEAR Scotland Southeast webpage (https://www.bearscot.com/se/), their remit includes.

"from A90 Dalmeny leading generally westwards for a distance of 1 kilometre or thereby to A90 Scotstoun Junction/M90 Junction 1."

This hilariously unspecific language suggests that about half of the distance from Scotstoun Interchange to the B924 junction is trunk. I notice there is an overhead gantry at about the 1km mark east from Scotstoun where there is also a change in road surface but no signage to indicate the start of a trunk route