Bren Gun Carrier
Tracked vehicle used by British and Commonwealth forces in the Pacific, including British, Indian, Malay, Australians, Chinese, New Zealanders some even by the American forces.

They were built by National or State heavy engineering firms or railways workshops, thus including Ford Motor Co. as they had heavy engineering workshops. Also English automobile manufacturers, also made in great numbers in Australia, Canada, New Zealand and USA (where it was known as the T16).

There were five main models built in Australia for Australian forces. Those being LP1, LP2, LP2A, 2 Pounder Tank Attack and 3" Mortar Carrier.

In Australia, carriers were mostly used in a training role somewhat like the Avro Anson or CAC Wirraway. Some definitely saw service in the Middle East and PNG, Singapore, Japan and Korea, but I am not sure of use in Milne Bay so I won't comment on this.

LP1
LP1 was the first unit manufactured. They were tiller steer, controlled by operating a pair of levers connected to the braking system. Powered by a Ford V8 side valve engine of 95 horsepower driving through a standard Ford four speed truck transmission to a Ford diff with a ratio of 5.83:1. However these units were found to be difficult to handle where a road only took a gentle but sweeping turn. All 160 units were built by the Victorian Railway Workshops in Newport

Local Pattern 2 (LP2)
Australian built machine gun carrier. Bren Gun Carriers were allocated to all types of Australian Army Units. Within the Armoured Corp, they were used by a number of units. Owing to the shortage of tanks, in the newly formed 1st Australian Armoured Division (1st July 1941), a great number of Carriers were pressed into service to provide tactical training for tank crews in Milne Bay and Cape Endaiadere near Buna, where their attack failed with all destroyed on December 5, 1942.

LP2A
Improvements were made and LP2 was designed. With more improved hull design which included fully welding the hull for better strength. Still powered by the same engine and transmission setup, until changes were made by Ford for the fitment of the rear axle and the model LP2A was designated. The later also having a diff ration of 6.66:1. Of this unit some 5000 were manufactured by five manufacturers 1 Victorian Railways at the Newport Workshops, 2 South Australian Railways at the Islington Workshops, 3 Metropolitan Gas Company, Fitzroy, Victoria, 4 Ford Motor Company, Broadmeadows NSW, and 5 State Engineering Works, North Freemantle, WA. The later only building 100 units upon cessation of manufacture by all other builders.

2 Pounder Tank Attack
The Tank-Attack or 2 Pounder carrier was built by the Metro Gas Co, to fill a gap as self-propelled artillery in the Anti-Tank role. Only 200 of these where built. The engine being relocated to the front left of the vehicle ( a position usually reserved for the main armament of these type of vehicles, The Bren ). This allowed for the fitment of the 2 Pounder Anti-Tank gun, firing a projectile not too dissimilar to a Bofors 40mm Anti-Aircraft round.

3" Mortar Carrier
The final was the manufacture of 400 3" Mortar carrying Carriers based on the 2 pounder hull, but with the mortar in place of the Anti-Tank gun. Also built by Metro Gas Co. all of these were given to China and not one of this model is known to be in existence today.

References
Thanks to Pedr Horley for additional information.
Pedr Horley adds: "Australian Military Equipment Profiles, Volume 2 Local Pattern Machine Gun Carriers" by Michael K Cecil is a fantastic resource on this topic or if you want more detail on the overseas built variants I suggest "Universal Carriers Volume 1" by Nigel Watson."