I had this same question a few weeks ago and I have found that most people say it doesn't matter, but I think that somewhere the answer is known, engineers are too picky about that kind of thing for it to not be an issue and there has to be a certain way they go. I pointed mine up, so that the drain-off would kind of allow the oil to cover the lifter bore evenly, using gravity as a benefit, even though that I think it really doesn't matter because of oil pressure, I just wanted all mine facing the same. The other reason I think it may matter though, is because the chiltons manual says to mark exactly how they came out, and they had to be in there a certyain way.
I would hope he knew that. J/K Most people do say it doesn't matter but I agree with saleenx029, it doesn't hurt to face them all in the same direction. I always go with the shortest distance to the lifter bore galleys.
I dont remember if I payed attention to lifter position when I put my engine together. I think it was probably random and my valvetrain is still quiet.
There is a large groove going around the lifter that the oil hole feeds from. That groove fills with oil from the gallery so no matter what way the lifter is turned it still pumps up. Flat lifters are actually meant to rotate in the bore and they look the exact same externally short of having a roller on the bottom.
engineers are too picky about that kind of thing for it to not be an issue and there has to be a certain way they go.
It would be in their best interest to make them universal. It would reduce the possibility of warranty repairs if the assembly line lifter installer got one backward and it didnt burn up the valvetrain until 50 miles after someone bought the car. I got some defective lifters from PAW(PAW brand I might add) years ago and it took about 75-100miles to cook the pushrods and rockers. The hole in the pushrod cups wasnt drilled all the way through in more than half of them.