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Tankers hated those radial engines. They were too tall and made the tank siluette taller than they wanted. And you couldn't run them at idle or the plugs got dirty too fast. There was a major supply operation involved just in getting the plugs sandblasted. In normandy they just sifted beach sand I think. It took well into the war before deasil operated in line engines were made to fit them. Only reason they used the aircraft engines was they were in ready supply. Which probably killed thousands of GI's of the course of the war.
I hadn't heard that particular account that tankers didn't like the radial engine because it made the vehicle too high profile however, I suppose there could be some truth to it being that the drive shaft travels under the turret basket. Assuming the the drive shaft angle could be reduced with a v or inline engine the basket possibly could have been lowered 8 or 10 inches. Interestingly the M5 Light Tank has a very similar profile to he M3 Light Tank (above) and is the same height despite having Cadillac flathead V8s. It has a redesigned hull and was the next iteration of the light tank. The largest complaint of the light tank by far was the lack of firepower. The 37mm gun was worthless against most armor in the ETO and shifted use to the PTO against the equally ill equipped Japanese tanks and gun installations.
M5 Light Tank
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The M3 Medium Tank (General Lee) which had R975 had a very high profile but it had little if anything to do with the engine and was the result of the strange armorment configuration that had the turret mounted 37 mm on top of the already high profile hull that made room for a flexible mounted 75 mm gun. They didn't see much front line action after North Africa when the M4s came on the scene.
M3 Medium Tank
M4 Medium Tank
The M4 Medium Tank (General Sherman) also had the R975 engine and had a reduced profile from the M3. The perhaps could have been reduced slightly by inches perhaps if the drive shaft angle could have been reduced giving the turret basket room to be lower however subsequent models employing V or inline engines were all similar in height, although that could have been due to the desire to keep the hull similar in design for parts, although there were already several hull designs.
From the documentation I have read it appears that both the British and the Americans considered the R975 and R670 engines reliable. The biggest complaint about armored vehicle engines in general is that they took 80 octane gasoline as opposed to the 68 or 70 octane that you could use in a jeep or 2.5 ton truck. I'm also am not sure that the aircraft engines were used because they were in ready supply as the main reason the M5 Light Tank was required to use a non aero engine was due to supply issues. It was also one of the reasons for the redesign of the M4 to the M4A3 to use a Ford V8 besides the additional power. It was probably due to limited engine designs at the time that could reliably and somewhat efficiently generate enough horsepower. One thing I can confirm is that the use of gasoline engines was a serious problem as any serious hit would turn into an inferno. Unfortunately, not enough M4A2 and M4A6 with diesel engines made it into combat.
The American tanks were under armored, out gunned and tiki torches compared to the German tanks however our hydraulic turrets, sheer manufactured numbers, gasoline and ammo supply lines, and some brave young men were enough to keep us in the lead.
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