In the old days it was standard procedure to take the block , during a rebuild, to the "vat".... and they would really clean it out.
I suspect that that is not done in most cases with these old diesels... and anyway.... an old gas engine was likely to need a rebuild at half our engines mileage/age.....
So if you take the radiator out and are really trying to have it in the best shape you can I would suggest taking the core plugs or freeze plugs out... and using a 90 nozzel on a pressure washer to break what you can loose... and keep flushing until it is clean water coming out. I don't know if any access hole exists on the drivers side....