Make sure the driveshaft is running true before you have it balanced.
They don't always need to be balanced, but when they do....

Check your tires for out of roundness as well.
Usually not a problem with todays tires, but it happens now and then.
Might check wheel runout as well.

All of this checking can be done with a screwdriver balanced or taped onto a jack stand, turning the item to be checked by hand and seeing if it runs true or not.

As far as your header touching the steering box, not good.
For the heat problem at the box among other things, but that contact will magnify any vibration coming from the engine.
Note the rpm at the unbalance point.
Stop the car, put it in neutral, spin the engine up to that rpm and see if the vibration comes in.

Another one you can do is get up to the speed where the vibration comes in and slip the trans into neutral and coast for a little bit.
That will tell you if the problem is in the engine or drivetrain/wheels/tires combo.

Do a little investigation before you drag your wallet out....