That's fine with me too.
Since the park boundary is legally at the south end of Gardiner (where the buildings that front Park Street are), here's another proposal. Based on the convention that there are no US routes within the park, US 89 gets truncated to 2nd and Park (where the MDT 0 mile marker is), NEntRd is extended along Park Street to 2nd and Park, and the connector gets added as a new usanp route ("3rdSt"?). Alternatively, we could move the US89 endpoint to 2nd and Park and add "ParkSt" and "3rdSt" as new usanp routes. These are just spitball ideas, by the way.