We are at a critical point in WWII warbird ownership.
There are few Merlins available and they are flying parts today that they would have thrown away 20 years ago.
There are no P-51 Mustang propellers left (actually few ...) and if you want to make a new P-51 prop, you need to buy both props from a Grumman Albatross, and use two balanced blades opposite from each other for the four blades.
Curtiss Electric props are also a bit scarce, as are accessories. We can work on Merlins, too ... but usually don't. Many Alilison / Merlin / DB600 cases have spun bearings and you have to line bore the case to rebuild it. We can DO it, but not many people can because the tools are getting increasingly scarce. A good line hone capable of honing a Merlin, Allison, or Daimler-Benz is no longer made. You need to find an old one and overhaul it. We found one in average shape and spent 3 months overhauiling it. It is pristine now and we can line hone WWII V-12's. Not many shops can make that claim.
If you spin a bearing, the case is usually lost to the world population. What you do is to drill out the bad bearing race bigger than stock, weld it back to smaller than stock, drill it back to just a small bit smaller than stock, and then hone it back to stock dimensions. If you have the machinery and the know-how, you have just rescued an otehrwise useless engine case, and can return one to service. WE can, but not many shops can or do.
Increasingly, the warbirds are the perview of the ultra wealthy because the parts are so scarce and expensive. That's OK, after 70+ years, maybe it's only the way life goes.
The point is, yes, WE happen to have Alllison engines available, but they aren't cheap or easily rebuildable. If we start with a complete Allison, we can usually rebuiltd one in about 6 - 8 weeks unless the schedule is full. Then the timeframe is variable depending on the backlog.
So ... enjoy them while you can because their time is limited. When the peoplpe with the knowledge to overhaul WWII V-12 and radial engines in bad condition retire or pass way, the skill is lost and the engines become unsupportable. The same is true for propellers and other critical parts. For instance, all the parts for Allisons (and other WWII engines) that will ever be made HAVE been made. When a water pump shaft is worn, we don't throw it away. We send it out to be machined down, replated, and then remachined back to stock specifications.
My own estimate is we can expect to see WWII fighers flying around for perhpas another 40 years and it will be done becasue the parts and skills to keep them flying will simply be gone.
I am 61 years old and the younger generation simply doesn't care that much about WWII aircraft or even flying in general. WWII WAS 70 years ago. So even though the hulks are rebuildable, there is little modern desire to do so from young people. We see it at the museum ... we have 300 volunteers and maybe 10 -15 are younger than 40 years old. And they usually don't become A&P mechanics or even get pilot's licenses.
I've had a good go at flying and have flown Cessnas, Pipers, Stearmans, and even have a bit of time in a MiG-15 UTI along with some VERY unusual time (got to fly right seat for awhile in a Convair 580). We even restored and got running a WWII V-1 pulsejet (Google Chino Pulsejet and you can see my pickup being pushed dowbn the runway with the pulsejet). I wish the younger generation had more interest in it, but they seem willing to fly on a jetliner with a computer for a pilot. Not me, ever.
I grieve for the great birds when our generation is gone. A Spitfire or Mustang should be flying once in awhile, not static in a museum with dust on it.