Sigur, not to burst your bubble or anything, but since you are pressed for time, your best bet is to get a 280Z or 280ZX motor and just do an easy drop in that will run for a while. Should be the cheapest way to go too. The worst thing is to find out that the V8 conversion will cost more then you estimated or take longer then you anticipated. You'll have to deal with a nonrunning car, or no money, etc. or a combo of a lot of things. This is the kind of thing you do not want to rush. If you had all the parts now for a V8 conversion, had solid quotes from competent professionals, and it was within the timeframe you set for it, you're fine. Otherwise, you're going to be screwed.
You are actually better off putting a 280Z longblock in the car, selling it, and then buying an already converted V8Z. That might sound painful, but that is reality! I'm not saying this to discourage you, but just to give you a healthy bit of reality and history of what we have seen time and time again. Don't lose the car over your desire to do a conversion--beware!!
Davy