Thank you all for offering perspective and possible solutions... this is what i think I will try, since I am trying to keep radiator as far "forward" (away from the engine) as possible...
I am going to use the 1/8 rubber washers that I have today, but I will create a "sandwhich" of (metal washer, rubber washer) in front of the radiator mounting flange and (rubber washer, metal washer) behind the radiator mounting flange, that will solve the "mixed metals" issue (aluminum in contact with steel) as well, except of course, for the steel bolt going through the entire stack.
