Thanks for your very knowledgeable reply CalBear. Ah, pitty is midnight again as i like going on and on about this stuff.
I am just assuming for the purpose of this TL that there have been carrier engagements and IJN carrier strikes after Midway, but somehow despite having ships damaged the IJN lost none (except Ryujo). They do have increased fighter squadrons of 27 Zeros on the large CVs. Conversely i "accelerated" the commission of and extra Essex and Independence by late 1943.
The IJN carriers are Akagi, Kaga, Hiryu, Soryu, Shokaku, Zuikaku, Junyo, Hiyo, Zuiho, Ryuho screened by 7 BB (no Kongos lost), a dozen CA/CL and two dozen destroyers.
Airgroups for the large carriers (Akagi, Kaga and the 'kakus): 27 VF, 27 VB, 18 VT plus couple of VS each.
Airgroups for Hiryu and Soryu: 21 VF, 18 VB, 18 VT plus one or two VS each
Airgroups for Junyo and Hiyo: 24 VF, 18 VB, 9 VT each
Airgroups for Zuiho and Ryuho: 21 VF and 9 VT each.
Most of the VF will be A6M2/3 with an important number of A6M5 being fielded as well. There would probably be a number of D4Y1/Y1-C and B6N1 Tenzans on the larger ships, complementing but not replacing yet D3A2 and B5N2, but the second line carriers are equipped with D3A2 and B5N2 only.
All IJN large carriers would have somewhat increased numbers of 25mm AA, improved damage control, most have radar, and Akagi has 12x 100mm (3.9 in) type 98 AA guns refitted during second half of 1942 (not sure if pushing it here, Akagi was intended to be refitted with apparently 127 mm type 89 guns, but someone suggested why wouldn't they go for the newest and most capable AA gun?)
Ozawa is likely in command (how long can they keep Nagumo anyway).
PS: Oh wait a minute, it might be Yamaguchi, not Ozawa.
The D4Y was a serious problem in development as well as once in the field. It had a number of great features, especially over the D3A, but the chances of them being the main, much less only dive bomber operating from the big decks is minute, and if they were somehow deployed, it would have a major impact on availability (as was the case with all the post 1941 Imperial designs the Atsuta engine had serious reliability issues, mainly related to the actual metals available for construction, eventually the engine was replaced by a Mitsubishi radial, creating the Model 33 but that was well after the scenario date, and the swap created some other insoluble issues, although it had the advantage that it ran more reliably). While the B6N was more reliable, it also suffered several delays in production (one related to an engine swap after only around 130 were completed).
It is strikingly unlikely that the IJN would be able to get these problems straightened out, especially for both aircraft, in the time frame under discussion. It would actually be easier for the USN to have the carrier force fully equipped with Corsairs, than for the IJN to have even partially full decks of Suisei.
The Japanese were also very unlikely to replace the 127mm guns on
Akagi with the Type 98 100mm, if for no other reason the relative scarcity of barrels (only 163 were produced during the entire war). It is a minor point, even a dozen addition 100mm are unlikely to have more that incidental impact, but the IJN didn't do things quite that way. Even with the 100mm the train rate (16 degrees a second, compared to the USN 5"38 rate of 25-30 per second)) of the mount makes it a far less capable weapon than its pure ballistics would indicate. The general increase in the 25mm guns is rather like the USN mania for mounting 20mm guns on every available flat space, having the gun there is an improvement over nothing, but that is about the best that can be said for the small caliber weapons.
Regarding the BB screen and the inclusion of the
Hiyo class ships - This mean the
Kido Butai is now limited to ~25 knots, even under ideal conditions, less if any sort of weather is encountered since that is the top speed of the
Hiyos. The battleships are also of minimal use in the AAA escort role, although being as large as they are they might distract some pilots from the carriers, despite the emphasis placed on the mission by the CAG.
Lastly, had Midway not sorted out the way it did, Nagumo would have remained in command of the
Kido Butai, unless Yamamoto had been killed, then he might have been part of a general promotion shuffle. Having won at Pearl, Midway, in the IO, and in every other carrier/carrier engagement (in fact the ONLY time the IJN lost a deck in this scenario was when a carrier force went into action without him in overall command of the strike force). He would likely have gotten the aura of invincibility and unfailing luck around him, something that would weld him to the command chair.