Not sure which parking lot you are referencing Carter. Here is a map of walker ranch, which shows the one I was thinking of.
The parking lot is at Ethel Harrold Picnic Area and Trailhead on the map. Shuttle is about 5 miles via flagstaff road from put in, so shuttle is much shorter. Trail is river left at the bridge drop up to the parking lot.
I agree with Joe that missing out on the last 3/4 mile of whitewater would be a bummer. But if you are looking for a quickie, its a 3 mile run, 5 mile shuttle with a mile hike out that route.
Nice idea to try and secure access to the road to the dam.
Still thinking about Friday down to the dam. Anyone?