Dunoon was one of the first sites in the Highlands and Islands scheme, with installtion of the link to Scroggy Bank starting in October 1970. The standard "Type 4A" tower is at the telephone exchange which itself appears to have been built in the late 1960s.
The original Highlands and Islands "network" was largely a set of point-to-point links at 4GHz using STC RL4K equipment (Post Office designation RS 10/29). The RL4K was solid state with 1 W output carrying 300 telephony channels. It was to be the last STC microwave equipment to be used by the PO as STC decided to withdraw from the market soon after.
BT Archives does not appear to have any photos of the exterior but a colour image of the RL4K at Dunoon (undated) is available.
Ofcom data suggests a link still operates to Scroggy Bank but now at 6 GHz.