Waldorf: "Sounds like an imminent threat from the Soviets! Or worse, American mothers demanding their sons be returned home ASAP!"
Statler: "Good luck with that, at least you can reason with the Soviets!"
Both: "Do ho ho ho ho!"
In very broad strokes, to restart Japanese industry so soon after the war would require a very large investment just to rebuild the towns and cities where you intend to build/rebuild the factories. Adm. Fischer has bullseye'd what the initial situation would be, Korea really was the catalyst to jumpstart the rebuilding of Japan's military. To be needed so soon also means that a 1946 Japanese military might not be restricted to self-defense, with the expectation that they were needed now for use elsewhere.
That said, if you really did need a crash program in 1946 it would probably involve the US transplanting training facilities and instructors to Japan and just recruiting locally, effectively making a mirror of (and under the control of) the US armed forces for maybe a decade before the official hand off to a reformed Japanese general staff. With war tribunals still underway the Japanese Armed Forces would probably have almost exclusively American officers until enough local officers have either cleared training or been vetted through the tribunals.
Restarting the aircraft industry with indigenous aircraft designs might work, perhaps with engines imported from the US, but surplus aircraft are available in increasing numbers so Japanese industry would probably start by making parts for them, unless Japan has a design that fills a niche that can't be filled faster with imports (maybe a seaplane). As mentioned, you'd need a new training school to basically start over from scratch, Japan was really scraping the bottom of the barrel by the end of the war when it came to pilot training. I remember reading somewhere a contributing factor to the high failure rate of kamikaze attacks was that the pilots were just that terrible they couldn't be expected to fly straight.
Ground vehicles are in a similar situation: building trucks and cars locally would work, fighting vehicles are best imported. Japanese tanks are not held in high regard for good reason, whatever their virtues.
Small-arms could be manufactured locally, but to US designs. There are enough surplus M1s lying around Japan might only make ammunition for years.
Any ship building for a Japanese Navy would probably be limited to repairing/refurbishing ships from the war deemed suitable for immediate use (probably limited to destroyers and a few cruisers at best, I think Takao was still in decent shape at war's end, say 'hello' to the new flagship). This is the one area I think Japanese designs would be used from the outset, just because the hulls are available and haven't been broken up yet by 1946. I doubt anything bigger than a destroyer will be built locally for years, if they really need anything more, they'll (say it with me now!) just use American surplus.
Honestly, the more I think about it the more I think a 1946 JAF would just be the local branch of the US Armed Forces with American officers and equipment. I'm not familiar with the history of the JSDF but it might hove even closer to the US model for the first decade or so of its existence before even being recognized as a unique institution in this scenario.
