Fire up the TIG welder and stick the two bits together all the way around. Any local metal fabrication shop should be able to do this for you if you don't have your own welder.
Line up the mounting plate on the same mark it was cut off from and check with the mount bracket that the angle is correct. Once happy with the position weld in place.
Now the time consuming bit. Start with course wet and dry and sand the whole assembly to remove all marks. Work through finer grades of paper to achieve a semi polished finish. I finished mine on a buffing wheel attached to a bench grinder.
Refit pipe to car. The mounting bracket needed the holes sloting slightly to allow the mount to fit without twisting the rubber mount. Stand back and admire your handy work with a beer in hand! Dont forget to do the other side though!
Craig.