Their informant was talking through his hat
Danny, I'm afraid I was at cross purposes in talking about Allison engined aircraft rather than the A-36 in particular. The Brits never used the A-36, other than one test aircraft given them. Wing Commander Peter Dudjeon a former Mustang1/1A CO performing "Rhubarb" raids was the man.
Seems that it was first built on contract for the wartime British Purchasing Commission
Yes, actually the British wanted to buy more P-40s, and asked NAA to licence build them, but NAA came back and said they could build a better aircraft, with the Mustang being the result. The British paid the hard coin to have the aircraft designed, built, and bought 620 prior to lend lease kicking in. Without the British there would have been no Mustang.
The Mustang was to replace the P-40 in the low level role with the Army Cooperation Command, so the performance of the Allison was no handicap. The Spitfire was the Air Ministry designated high altitude fighter.
what's all this about the Allison being more reliable than the Merlin?
More robust Danny, not more reliable. The RAF removed the automatic boost control on the Mustangs. This allowed a sea level full throttle 72", rather than the take off 45.5" or 56" war emergency. And they ran at 72" for up to 20 minutes in combat. The bearing life was 1,500 hours vice 5 to 600 hours on the Merlin.
Mustang racers at Reno invariably use Allison connecting rods in their Merlins. They have a much larger cross section, and a better bearing design than the stock Merlin rods. These Merlins are putting out as much as 3,600 HP at 140 to 150".