I am putting in a 1970 350 into my truck. The engine has never been apart and was designed to run on regular (leaded) gasoline. I have been told that I might burn a valve/valve seat or that the valve guides might stick if I run on unleaded gas. They say that the valve seats are not hardened and that the guides need the lead to lubricate them. They also told me about an engine like mine ran on unleaded for 30 minuets and burnt valvles and bent push rods because the valves binded. Is what they are saying true? Is there a fuel additive that I can get that will enable me to run on unleaded?