I really want to thank everyone that has contributed to this thread thus far. It's been incredibly helpful to me, and I've learned a lot!
Until FFR releases more details on the kit, I can't make any final decisions, but I'm thinking 1 of the following 2 options is likely:
1. Buy the basic kit and obtain an '07 WRX as a donor. If possible, outfit it with an STI turbo and tune.
2. Buy the complete kit and source an '07 STI engine and an '07 5-speed transmission (which if I understand correctly, should hold up OK).
I'm leaning toward #2 if it's not out of my budget because it uses more parts that would be new, and eliminates the need to remove said parts from the donor (making it "easier"). Still, according to folks on this thread, either way should be good for around 300 whp - less than I really wanted, but based on what I've learned, it's where I should be to meet my primary goals. If newer components wind up fitting OK, I would prefer them, but I don't want to have to fabricate or make any serious alterations to do it.
Again, a sincere and heartfelt thanks to all of you. You've been great.
And this thank you is not a call to end the thread by any means! I'm sure I'll continue to learn more as the discussion continues.