me personally i wouldnt run any gas in the engine. Yes some people have done it and thats great, but to me its not worth damageing the engine. I would instead use power service and clean the tanks.
Personally I would take this /\ /\ advice. After you clean the tanks (With your Bro's help) dump in a whole gallon of the Power service in about 5-10 gallons diesel. Of course change the duel filter first, then change it again after burning that tank. Gasoline will/can coke up the injector tips. Read this article.
http://www.turbodieselregister.com/mixing_gasoline_and_diesel.htm