I would do two things. One you may have already done - put a rebar in there and fill the pipe up with ready mix concrete.
The other thing I would keep in mind is that a lot of the stress in wind will be twisting stresses. I'd consider running a weld around the curved end of your u-bolt, welding it to the mast.
After you get the dish aimed perfectly, I'd also mark the bracket and the mast with a punch. I wouldn't honk down hard on any bolts connecting the dish bracket mount to the mast. If it wants to twist, the dish and bracket will turn and the mast wont twist and get destroyed. If the dish twirls in the wind, just wait for a calm day, go up there and line the punch marks back up. This has been my method on my two big dish installations. I'm near the mountains and definitely get wind, Still, I haven't ever had to line my marks back up because of wind.
My installation is similar to yours in that the mast goes from the ground and is reinforced by the eaves and then goes about 5 feet above the roof line. It's just an added level of comfort, me knowing that, if a big wind twists it around, i won't have to replace an entire mast.