Hey Scottly,
You might consider taking Hwy82 (just past the TX - OK border) west to St. Jo. In St. Jo, you can pick up hwy 59 south all the way to Jacksboro.
In Jacksboro, You can hit 281, like you have planned, all the way to Burnet.
I-35 through Denton to Ft.Worth can get congested and a bit crazy depending on the time of day. In fact, I try to avoid the interstate as much as I possibly can.
I'll admit I am far more conservative than I was in my youth. Just don't care for the cagers much anymore.
Might just be me, but I definitely prefer quieter / less traveled roads. It would probably add an hour to the riding time, but it would offer easier places
to pull off and rest etc. More peaceful and less stressful as well. Been a long time since I took a ride down to Austin, but that was the route we always took.
Another bonus: In St. Jo and some of the smaller Texas towns, you can actually buy gas without ethanol.
Again - this is just my 2 cents. You guys are doing a great thing here.