Its a friendly level right now, but blackrock rapid had some rocks shift a bit with high water and has some sharp stuff now in the upper half.
My advice would be that if you are stepping up to the black rock run, you should just do that--i.e., put in at the normal put in a few pull outs above black rock rapid. Running dumont down will leave you tired when you get to the run, especially since it is slow and low now. I'd save the marathon run for after you have run black rock successfully and are comfortable with it.
As for the nature of the run, drive up and check it out.
My advice would be that if you are stepping up to the black rock run, you should just do that--i.e., put in at the normal put in a few pull outs above black rock rapid. Running dumont down will leave you tired when you get to the run, especially since it is slow and low now. I'd save the marathon run for after you have run black rock successfully and are comfortable with it.
As for the nature of the run, drive up and check it out.