Motor mounts - I'd replace them if they look bad, but other than that I'd just get them lined back up. I have a set of small block mounts and they have a little bump on the mount that rides in a hole drilled into the motor mount brackets to keep everything pointed in the right direction. You may have the same thing as I do only yours got tightened down with the nubs out of the holes which is how yours went sideways.

Your car has a manual transmission so you'll want a torque strap or something to help secure the drive's side as that's where the action is. You can buy one, make, one, or overhaul your rubber driver's side mount and convert it to a solid mount with some steel and welding.

I would get the mounts straightened out one side at a time and work with shims and see what happens there first before messing with denting the header right away. If you do have to dimple the header tube you'll want to dust some silver header paint over the spot to keep it from rusting. In my mind having a header tube just barely touching the steering box is not the source of your drone sound. I think that is coming from the mufflers on back and is magnified by having an empty trunk compartment.

If you want to switch to side exit exhaust then look at the Dr Gas NASCAR style mufflers/exhaust tips. I think they would be fairly loud compared to rear exiting, but they may not drone. They are pricey, but offer the best look for that type of exhaust setup. Having a round pipe sticking out in front of the rear tire doesn't look very cool in my book.

https://www.youtube.com/watch?v=jucWtepx6PU