if I saw it right, what those pictures show is that the old tub used to have its P trap aligned pretty much directly under its overflow hole, and not directly under its drain hole. The pipe coming almost straight down from the overflow goes into the P trap opening. There is an offset in that vertical pipe.
Then, I think what hj said is that ya gotta align that P trap opening now to be directly (or with that slight zigzag offset) to be under the new tub's overflow hole. Like the current set up.
Then, what Jimjadnashau said is that ideal would be to put the P trap opening directly under the tub drain hole, which is very often seen, and always advised when possible. The small problem he mentions is that organic matter can stick to the piece of pipe before the P trap, like hair and gray water sediment dust. Not a serious concern, imho.
Although you have very little wiggle room, you do have some. Pivoting the P trap so its opening is under the overflow hole, or under it with a slight offset, seems to be possible, if i read hj's remarks right. It is a couple inches over but it doesn't put your P trap under that concrete.
If this makes sense, then i am happy.
david
