FYI....almost any engine can be run safely on unleaded fuel. The only concern would be in vehicles used for towing or competitive racing. Its all about the heat,not the material used for the valve seat or what fuel you use.
Yes back when unleaded fuel was first publicly introduced there was a lot of bellyaching about the damage that could result all of which over time proved to be an old wives tale. The simple fact is no matter what your valve seat material is it will get a good hardening during your engines break-in regardless of if you know how to do it or not
The cooling attributes of lead deposits on your valves and seats proved to be more of a detrimental effect on valve train durability. In the end it was found to be the oil's and the fuel's cooling effects that really mattered. One more reason why direct injection finally wins over the carb!
but ( after 1st removing all the fittings ) I have cleaned various tanks out by 1/4 filling them with wet gravel and sand , and giving them a good shake about , aparently steel shot is the go but I didnt have 10 kilo's of that
, in the sun( 
) so much lately