I can't speak for the Reserve to AD part of the question, but the UPT part I can comment on. If you get a pilot slot from OTS, then the track select after T-6's at most bases gets you to the type of aircraft. The same thing happens again when you finish T-1, T-38, T-44, or rotor training (Sheppard only has T-38's on base but now has the option to send someone to T-1 or to Corpus for C-130 track which has been exercised a few times). You fill out a dream sheet with your choices and then get matched w/ an assignment (the higher your rank, the more likely you'll get a top choice, but it all depends what the class has to choose from). The only constant these days is that things are constantly changing in the rated world.