Since Tom H has used my name a few times I guess I'll chime in now that I'm back home after rating a course today, unfortunately not one that is anywhere near the league of Oakmont. This will probably be quite long as there is a lot to answer.
We will be rating Oakmont next year some time when they get all the changes in place. First let me say that most of the changes being made are based on an aerial photograph from the late 1940s which was when Mr. Fownes died so it probably reflects his thoughts. The only area where they seem to have done something a little odd is that they really pinched in the end of the landing area on #14 to force the driver out of the big hitter's hands. The adding of length will restore similar shot values to most of the course. I have an ad from an old American Golfer that talks about the 15th at Oakmont being a 475 yard par 4 in 1927. #9 will be played as a par 4 for the US Open. But who cares as par doesn't matter.
As for #8, if we rate the back tee separately we would probably rate it as a par 4. But, due to some possible changes in the course rating system next year, we might only be rating one set of tees for men and one for women in the future. Yardage differences will be used for all the rest. In that case, we would rate the most frequently used tee which will definitely not be the back one at Oakmont.
In the >100 courses I've rated, I can't recall seeing a par 3 that would be rated as a 4 from one tee. We do see the opposite quite frequently though. Today we had a par 4 that had a senior tee that was only 228 yards so we rated it as a par 3.
Tom H. you were 5 yards off on both the scratch and bogey golfers second shots, they are 220 and 170. Add 220 to 250 and the "maximum" for a par 4 is 470 yards. We certainly do encounter par 4s over 470 yards. There is no difference in rating a par 4 or a par 5 so it really doesn't matter what the club wants to call it. We also see a lot of par 5s under 470, especially on older courses. That also doesn't matter.
In regards to manipulating the course rating system, it wouldn't be hard. To get a higher course rating, tighten the fairways from 225 to 250. To get a higher slope, tighten them at 180-200 and again at 360-370. Or build a creek across the fairway 20 yards short of the maximum carry distance for the player you to increase. To get both numbers up there, grow the rough real high and get the greens real fast. Lots of other ways also. On top of that, by making holes of certain lengths just short of the 2 or 3 shot maximums for specific golfers you can get the numbers up.
I do know of one owner who really cares about his slope and course rating and wants the slope as high as possible. We got a call asking why his course had a lower slope than Pine Valley. We pointed out that the course rating was much higher and the bogey rating was higher, but the difference between them was less so the slope was lower.
Tom D, I'm glad you don't care to think about the slope system and I would hope that most if not all architects also do.
Tom H, as for the tiny % of players who can reach the 285 yard par 3, there won't be many players who play it at that length and I would assume that most of them at least think they can reach it. I know we didn't go near there two weeks ago when we played it.
Kyle, As for someone jobbing the system by building tees and never using them, when we prepare a course for rating, we look at wear patterns and try to find the middle of the areas that are being used. So, if a course that built a 50 yard long tee and tried to tell us to rate it from the back and we say all the divots and the like in the front would find we didn't do what they want. For new courses, we go back every 2-3 years for the first 10 years to make sure they haven't change things too much. Sometimes they will grow the rough real high at first and then when the see the effect it has on pace of play, the start cutting it shorter.