Are these trailheads closed due to road construction or trailhead reconstruction? Anyway,
@TheMountainRabbit 's Sepulcher Trailhead is the best option for an alternative. If for some reason that trailhead is affected too, then you could use the Bighorn Pass - Indian Creek Trailhead and use the old Howard Eaton Trail to hike north to intersect with the Glen Creek Trail.
Here is a map of where the trail runs on the ground. It would add 3.8 miles to your first and last days.
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Now knowing all of this, the old trail is easier to pick up on the Glen Creek Trail side than the Indian Creek side, but even if you can't locate the trail right off the bat, the off-trail you would be doing is pretty easy. There are old downed trail markers along the way once on the old trail.
The terrain looks like this -
Old Howard Eaton Trail between Glen Creek and Indian Creek
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Looking down on Swan Lake for the Howard Eaton Trail
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