I wonder if it would be worth trying 205 down to 80, then 429 up to Quinlan and back down 751/3815. I've ridden on 205 without issue. There is a pretty wide shoulder there. That route might actually make it longer than 100, but it might be worth it.
Or you could even take 276 over to 751 and cut out 205 entirely. I've ridden 276 as well, just not that far East.
One thing to note, you've listed 66 over the bridge into Rockwall. Depending on when you do this, it's better to use the walking path on the North side of the bridge to get accross. But be wary of glass. Sometimes it's fairly clear, other's it's like a minefield.
Steve