Mikes diagram is irrelevant in this case as the Notam describes where you turn base, which is no where near as shown on that diagram.
The 500' vertical separation is also irrelevant as we're talking about lateral separation.

Kyle is correct, there is at least 1/2 mile separation, between base and final for the two runways. If you want to fly into Oshkosh, you're going to have to reduce the distance between planes at times.
Be on your toes with your eyes open, that's the way it is.

Be careful turning a low and tight base to final to 18, too many guys have died turning too tight, I've seen it happen myself.