Yes. They originally turned inward and the plane wouldn't take off! They reversed the engines and things went well. Nothing wrong with the Merlins. Despite the protests to the contrary above, we don't have many problems with Allisons either, even 100-series engines, which most today are.
Both have occasional issues; many are self-inflicted. For instance, we had one Allison customer who disassembled his oil pump and nicked the seal when he tried to reassemble it. He had to send his oil pump in to the shop for work and correct shims since he dodn't note the shims as he disassembled it. When we asked why he disassembled it, he said he was curious about it! No training and no spares, but he felt qualified to disassemble an Allison oil pump without a manual or a parts diagram. I cannot credit that as an engine issue, even though his engine was down for a short while. We;ve had several who continued running the starter way past the safe limit and essentially melted the starter. Even cars have a "safe cranking time." If it doesn't start by then, stop, reassess, and try again. We even had one guy who drained his oil and proceeded to start the engine when a friend came over and let it idle long enough to require new main bearings!
Merlins also have occasional self-inflicted issues, so this in NOT uncommon, but also not frequent. Most people don't meddle where they shouldn't without the knowledge to meddle there, so it isn't a big issue ... and people who do it are embarassed, to say the least.
At the Planes of Fame, our Merlins run reliably, as do our Allisons. You don't often see our P-51's, our P-38, P-40, P-51A down for engine issues. The P-51A is usually down for radiator issues whnen it is down, not the Allison. We're making a new radiator of our own design ... hope that cures it! In fact, most of out WWII planes are very reliable.
In general, the Merlins and Allisons need different maintenance. For instance, every 25 hours you have to re-torque the cylinders on a Merlin. You NEVER have to re-torque an Allison cylinder assuming it was done correctly in the first place ... until you disassemble it and untorque the cylinder hold down nut. You would only do that when you change cylinder liners. But that is not a knock on the Merlin or a point for the Allison; it is a design choice with design maintenace requirements. Neither design is superior to the other ... they are just slightly different.
The Allison valve seats are in the head itself and never change height unless they are ground for seating purposes. The Merlin valve seats are screwed in until they break the franglble link and are then ground for seating. Again, neither cylinder hold-down design is better; it is a design choice. I DO like the Merlin's 2-stage supercharger bertter thanh the Allison supercharger - turbocharger but, in use, after the P-38's issue were corrected, it flew relaibly and well. The P-47 ALSO flew reliably and well with a turbocharger as the high-altitude boost system, as did the B-17 and B-24.
A few features of the Allison ARE better. The nose case is bolted on, so it can be changed from a prop shaft to a driveshaft for remote drive (like in a P-39 / P-63). The crankshaft and rods are much stronger than a Merlin's, but neither is weak at stock power levels. The Merlin's nose case is cast into the block, so it is difficult to adapt it to something like, say, a PT boat or a tank. They DID, but it was more difficult. The Allison was easy ... change the nose case for the drive you needed.
In the end, I think the Merlin proved a better engine in WWII field use in the ETO, but the Allison is a very good choice today for a warbird, assuming you can find an Allison-powered warbird, have the money, and are in the market. On the other hand, there is nothing wrong with a good Merlin warbird and I'd take a Spirtfire or P-51 if I had the means. Actually, I'd prefer the Spitfire despite being a US citizen. To me, the Spirfire, Bearcat, and Zero are the most asthetically-pleasing warbirds on the planet, but that is a matter of taste, and nobody needs to agree or disagree for it to be true. Your choices may differ, and that's just dandy.
I can't see affording a Zero since the population is so small. As it happens, we have the only one in the world running the original Nakajima Sakae 21 engine and Mitsubishi prop at the Planes of Fame, so the population is one plus a few other running American engines and propellers.
Gimme a Spit! Don't care what mark it is ... and don't care if the Merlin is British or US, either one would be just fine. I WOULD want a Rotol prop, though and a real Spitfire stick assembly that breaks in the middle, with the round grip. I'd put the radio push-to-talk on the gun trigger (MG, not cannon). I can dream, and it's only a lottery win away!
