Ummm...right, I don't mean to sound like an ass here...well scratch that, I really don't care if I sound like an ass actually...but anyways, why the hell are you buying a D15B swap right now if you plan to buy a B18C a few months from now? Why drop $500 on a motor and then some more bucks for a tranny, plus other miscellaneous parts and fluids you're going to need for the swap if you're just gonna do it all again a few months from now?!?
That sounds like a really dumb idea to me...just put your money towards the motor you ultimately want, and that way you can have it that much quicker. Four months isn't that long at all...
And no, you can't use headers with a turbo, at least not the kind of headers you're thinking of...
EDIT: I just remembered that this guy is temporarily banned from posting, lol... oh well, it'll be here for you when your vacation is over buddy...