You're not alone brother, not only do I have a well known (well, here at least) love for the Buff, I do love me some P-66. Always had a like for the P-43 with that big turbo in it too.
Well, rejoice! Because both the P-43 and P-66 were indeed used in combat, it seems. I like both of them too by the way. The P-43 is like a smaller, slimmer P-47, and the P-66 is also a very interesting looking fighter with, I think, some potential but which never got developed.
Sorry guys we have had a bizarre incident around here (someone intentionally sawed through a power pole with a chainsaw, knocking out power for thousands of people and one cable / internet provider) and I have been without internet for the better part of 3 days). I finally realized I could make a hotspot with my phone and that my desktop computer has a wifi modem so I am back for the moment, for better or worse.
Anyway, regarding the P-43 and P-66 use in combat. It's true that there weren't that many of them, but there were not that many of several Allied types in Theater - P-38, P-51A and A-36, Vultee Vengeance, Mohawk IV, Mosquito, Hurricane IID and several others were all pretty rare in terms of total numbers. So was the P-40K, arguably the most successful variant of that plane in this Theater. But they all played a role there, often an important role.
And on the JAAF side, Ki-45s, Ki-44s, Ki-46, Ki-49s and others were also rare but by no means missing from the combat reports, or lacking in relevance.
That's kind of part of what makes this part of the war so fun and interesting to read about.
On the flip side though, unfortunately, there are not a lot of good sources for this Theater, especially those which include the Japanese data, so we have to maneuver a bit carefully. I mainly have this Osprey book on the Ki-43 aces, another one (not as good) on JAAF Aces, and Shores Bloody Shambles III which I just recently acquired and am still reading. Shores is the best of that bunch but not without limits and omissions, and unfortunately, I think his focus was mainly on the RAF / Commonwealth units so he mostly ignores China, which is where most of the US fighter units were based.
There are also a few decent online sources such as
Pacificwrecks and
Aviation of Japan, plus a little bit of technical data on good old WWiiaircraftperformance.org (many, many thanks for this archive again, to the people who did it, who I know are around here). But unfortunately not much on the Japanese stuff even there. I'll also give a shout out to Pacific Victory Roll which mostly deals with the IJN and the Pacific Islands but there are some relevant facts on that wonderful and very sadly now missing website, which we can still access through the (also wonderful) Wayback Machine.
That said, we do have
some data. As I said I'm still reading through Shores, and I happened to just open the book randomly yesterday I-Ching style, and I immediately noticed two bits relevant to the conversation on pages 30 and 31. Page 30, on the left, is the passage I had previously mentioned where Shores notes that they had no luck catching Ki-46 with Hurricanes, but (he reluctantly admits) the yanks did catch a few with P-40s. I'll circle back to that later.
Page 31 notes that on 25 October 1942, during a raid by Ki-21 and Ki-48, escorted by 30 x Ki-43s from 50th Sentai and 32 by 64 Sentai, among the Allied losses were (and this is a direct quote
"Also destroyed were two Republic P-43 Lancer fighters, recently delivered to the 51st for high altitude interceptions,"
The 51st he mentions there is the USAAF 51st Fighter Group, which as far as I know, had no Chinese pilots, not that I think that really makes so much difference.
Right after that Shores reluctantly notes that the
Ki-46 piloted by Lt Teruo Ikeuchi was shot down either by a US 25th FS P-40, or by British heavy AA gunners. This is all on page 31.