Thanks for yours, and an initial response.
> Early in 1937, the SA [South African] War Supplies Board became interested in a proposal by Ford Motor Company of SA, to build an armoured car based on the Crossley design adapted to a Ford commercial truck chassis. After countless delays the project was shelved and in April 1939 an order was placed in the US for 22 M1 Ford 6-wheeled armored cars. (pictured below) >
I am afraid you are wrong here. The American M1 6x4 armored car was built by James Cunningham, Son & Company in Rochester, NY. This wheeled AFV came in two similar versions, the T4, two units introduced in 1931, and the M1, standardized in 1934, with a dozen units built (it's not clear whether the pair of T4 cars were retro-designated as M1s). The vehicle's manually operated turret carried a .50-cal machine gun, with two .30-cal. MGs firing through hull ports; a later trial mounting atop the turret for one of the .30-cal. MGs gave the car a modicum of AA protection. At 15 feet (4.5 m) in length and just shy of 7 feet (2.1 m) in height, having a weight of 5 short tons (4.6 metric tons)---the car's armor plate varied from 6.4 to 9.5 mm in thickness---and equipped with a 133 hp (at 2800 rpm) V8 gasoline engine permitting a speed of 55 mph (88 km/h), the Cunningham armored car was a deal smaller, lighter, and faster than the British Lanchester 6x4 armoured car thoroughly discussed earlier in this thread. Unlike the Lanchester, a pair of low-slung spare wheels on freely turning stub axles, designed to improve the AFV's off-road mobility by assisting it over low obstacles and preventing it from bottoming out---and identical to those on the British Vickers-Crossley and Soviet BA 6x4 armored cars, among others---did little to make up for not giving the car a 6x6 power arrangement, i.e., with the front axle also powered.
The T4/M1 cars saw extensive field trials at Fort Riley, KS, by 1st Cavalry Regiment, and elsewhere with 7th Cavalry Brigade, likely including participation in one or more regional maneuvers and war games held annually during the 1930s. Because the U.S. Army purchased only a dozen or so T4 and M1 armored cars from Cunningham, it could gracefully retire them after the disappointing evaluation period, in contrast to the 35 Lanchester armoured cars that the British Army was forced to assign despite excessive weight and insufficient speed. In the American AFV, note one strange thing: although the experimental T4 had come with sensibly painted metal headlamp cones, the later M1 came with entirely chrome ones. These shiny domes would hardly have stood it in good stead, whether on reconnaissance in front of an advancing mobile army, lying in ambush, or part of the rear defense of a withdrawing army, with the sun's rays bouncing off the chrome. Of course, they would have been replaced or enamel-painted over, but one has to scratch his head over this regression from good tactical sense.
The Cunningham T4 and M1 6x4 armored cars, respectively (note the headlamps).
The Vickers-Crossley 6x4 armoured car, alluded to above. The turret-mounted Vickers machine guns could be pointed independently.
The Soviet BA-10 (later variants) and BA-32 armored cars---BA is short for Broneavitmobil---built on the GAZ 6x4 truck chassis (in turn a Ford design), were armed with a 45mm gun turret essentially identical to those on T-26 and BT-5 tanks. This gun could readily deal with lighter enemy tanks, such as those encountered at Khalkhyn Gol (Nomonhon) in 1939 and in the early phases of WWII. The thin armor of the BA-10, however, made tank fighting a perilous undertaking, and underscored what every AFV crew member of every warring nation soon learned as an essential survival maxim: get off the first accurate
shot. Best serving the BA series of armored cars was their speed: 86 km/h (54 mph), nearly that of the American M1. Given the limitations of these AFVs, by 1943 they had been divested of their gun turrets---which thereupon went to light tanks and armored trains---and then utilized as armored personnel carriers.
More on your other points, especially the Marmon-Herringtons/SARCs, tomorrow.