I recently got an 87 4runner that had a snorkel already installed, unfortunately its for an hj/fj 75 2h diesel or 3f petrol motor, so its on the wrong(passenger) side and the angle doesn't line up well with the body(not that that matters)
so now i can either do a battery relocation kit and try to swap the air cleaner to the other side or i can get rid of this snorkel and get the right one. So if anyone needs one for there hj or fj and has one for my runner im willing to trade.
but to answer your question, the back is pretty flat, but it has an angle to it that matches my fender pretty well, but to get it to line up right with the windshield and the hole that goes to the air cleaner you have the have the center(the bent section) run lower the the line of the fender.
ill try to post a pic when i figure out how to do it from my iphone.