How about the RAAF, really missing having guns on their Canberra B20s (as per the .50cals and 20mm fitted to the USAF B-57s) in Vietnam for the COIN missions, adopts the Pave Gat M-61 Vulcan in an Emerson turret (as in the video back on page one).
What I would really like is the RAAF, impressed with the Olympus Canberra demonstrator decides to order a Batch II from GAF using the existing jigs and fixtures, as a cheaper option than replacing them with V bombers. The B20s would be relegated to the RAAF reserve, training, reconnaissance and maybe ESM/ECM as well as possibly selling remaining aircraft to the RNZAF. While developing this improved version GAF becomes aware of the changes Martin are incorporating into the B-57B, in addition to those already adopted in the B-57A and follows suit introducing the rotary Bombay, tandem cockpit canopy and wing guns (4x30mm Adens though).
These aircraft serve in Vietnam along side the USAF and adopt the Tropic Moon III and Pave Gat mods converting them into extremely viable COIN and close support aircraft that remain in service into the early 90s, last seeing combat during Desert Storm in 1991.