Hi,About two years ago I asked Bill ( drgondog ) his best estimate how much sooner the P-51B could have started ops with 8th AF. There were more than just a few stars that would have had to align right and a certain Colonel getting hit by a beer truck was mentioned but in the end, Bill estimated maybe late fall early winter 1943, about five months earlier than it did. I wish I could find the post as he laid it out fairly well, if I have time I'll try to find it.
Interesting topics, "how early could so and so"? TBH, I suspect that many things happened dammed fast, but where some were actually slow off the mark, it seems to me that there were often reasons that could not have been avoided, in the real world.
With the P-51B, Be careful what you wish for! IMO, the big factor that got the Merlin P-51 versions into the top-spot was not just "The Merlin", it was really the fact that the re-engineering was done with the "Two-Stage Intercooled Merlin"! (OK, Aftercooled to some!)*.
As I read, there were serious thoughts about going for a Packard Merlin 28, or similar single-stage version, to speed things along for a British exported version. However, wisely, it was decided to hold-out for the full Two-stage engine, with the now-known superlative results! Possibly, if an early(er) change to a single stage Merlin had been produced for the Brits, maybe it would not shine so bright and might not have have been procured for the USAAF.
*Oh yes, really the two-stage Merlins do have some Intercooling.
Eng