Seeing the map of the Glacier Half Marathon route reminded me of the construction on US89 in that area.
The rebuilding of US89 for a few miles east of Kiowa junction will probably be ongoing for a few more weeks at least.
The construction North of Kiowa junction is going to last through the summer in some form or another.
They are completely rebuilding US89, rerouting major parts of it between Kiowa Junction and the South Fork of the Milk River.
I was delayed for 20 minutes waiting on the Follow Me vehicle last week.
You will not be able to bypass the construction using MT49.
Looks to me like there will be major delays on that portion of US89 through the summer.
So in my opinion, unless there is official news to the contrary,
Those coming from the East on US2, the West via US2( Spokane, Kalispell, the KGPI airport, etc.) and from the South on US89(Great Falls, Helena, etc.)
You would be MUCH,much better off going into/through Browning and taking Highway 464, a left turn off US2 as you leave Browning, to where it meets US89 1 mile south of Babb.
It's about 36 miles if I recall from Browning to junction of US89 in Babb.
From there, make a left turn and it's a 10 minute drive to St Mary and the East entrance to the park.
OR
Turn right and go 1 mile to the Many Glacier entrance road by the Cattle Baron Steakhouse.
Highway 464(The Duck Lake Road) is a good road with a 70mph speed limit. No traffic lights or stops.
Great views of the Great Plains to the East and Northern Rocky Mountain front to the West.
pete