Sorry to say gentlemen, very first chuck I did was a 4 jaw had a similar rim to the one shown (mind you better casting and finish), the trick is you turn the plate flat and the cut a slight relief in the rim that it just allows the chuck to slip on yet not bottom out on the center flat, this insures that you achieve max bore dia, otherwise you constrict the bore size. Again this was when I was starting out and I consulted with some old machinist (prior to info being available on the internet) and this what he advised. One important note is once you start this final step do not remove the plate from the lathe, all fitting and work the plate remains mount until you are ready to locate the holes for bolting it on (btw I didn't remove it and located everything using a straight edge across the bed, horizontal reference, and a drafting square, best I had at the time. A machine shop checked, drilled and counter sunk for me, did't have a drill press yet, only missed locating one hole by 0.0005")
Here is an example, see about 2/3 into the video.