It appears to me to be about 30 feet south of the current bridge. There is an excellent photo that belongs to the Arcade Historical Society in the later editions of Pietrak's B&S Book on page 146. It clearly shows the old PRR bridge and the under pass of the B&S. There is a train blocking the south abutment to the PRR creek bridge, so it is only a guess on the distance.
From the existing A&A R.O.W. looking north on the B&S, the tracks would have been perfectly straight going under the Pennsy. Below is a shot taken last week looking in that direction, but as you can see, it is extremely overgrown and you can't even see the PRR grade.
I also walked in to see if anything remains. I could see no mound or evidence from the top side. There is however a concrete box structure that looks to me would have been between the PRR abutment and the B&S underpass. In clippings from Arcade Herald newspapers from the era of B&S construction, there was mention that the B&S had to relocate the pump house on the PRR to build the underpass. It was mentioned that concrete for the new structure was mixed on site by B&S contractors. Below is a view of that.
There is a picture of the original PRR bridge over the Cattaraugus Creek in the Triumph VII PRR book on page 297. It is taken from such a view point that you can't tell much from it. Here is a photo of the current bridge.
When I look at Google Earth, there is a lot of growth in the images. If you follow the A&A line straight toward the PRR, you can see a line going straight under and to the back of the property that you mentioned. The B&S was low there and not on much of a mound. It appeared to be pretty close to creek. Following under the PRR to the Hurdville Road (still going north), the tracks would have crossed just to the creek side of the Cement Plant driveway. From what I saw walking around this time of year, there was just too much growth to locate any kind of mound. The underpass under the PRR was obviously filled in, so I doubt any wing walls or abutments still exist there.
I am sorry that I didn't post copies of a couple of the pictures I referenced, but I don't own them or have decent copies to work from. Hopefully this helps you a little.