Ok, here's a little more info for anyone who had trouble doing this and still having a dark line on the side of their picture:
I ripped my 4805 apart and of course my light tunnel was in 3 pieces. I didnt realize it wasnt supposed to be a perfect rectangle so I of course lined the pieces up so that at least on the one side, the pieces met perfectly with no overlap - like there's supposed to be. Well of course that left me still having my dark line, no matter whether I switched it upside down or not, and I was frustrated. After reading this whole thread (which I didnt do the first time, I assumed what was on the 1st page was enough, thought maybe the 2nd and 3rd pages were thanks and all the rest), I realized it was supposed to be shaped funny with some overlap (someone on here provided an awesome pic), so I had already krazy glued this sucker together like fort knox, so this was gonna be a problem. I basically broke it apart gently by prying it apart with one of the tweezers i was using. Of course I broke one of the mirrors right in half, which was a super-bummer. Anyways, once apart I glued that mirror back together hoping for the best, then glued the remaining piece in so that it was shaped the way it was supposed to be shaped. Finally, I figured I would have a satisfying picture again, and life would be good. Of course not. I overglued this baby so badly that my picture was still experiencing a little darkness in the top left and the bottom right. I switched it upside down, the same, then I sanded off some glue, and it got worse!! Then I switched it upside down again, the same result, then I sanded each outter panel of each mirror to a (you guessed it) mirror finish, and voila! No more darkness anywhere, life is good.
Moral of the story: If you're one of the people who tried this and didnt get the result - you put on too much glue or you probably made it into a perfectly edged rectangle. Dont do either, but if you do, then sand off the extra glue or break it apart (there's probably glue solvents out there but it was late and I was already mad) and get it back together again in the right shape without any extra glue on it. It works.
Thanks to all for posting this info up, if it werent for you I'd have thrown my projector in the garbage and bought something not made by In Focus. This is the 3rd time my projector has needed to be fixed (first two times were color wheel failures of some sort, but covered under warranty thankfully). Lame.