if the cover melted off i would worry about how hot the cam was before they put the fire out with water or what ever they used ? as the water would hit the cam in some spots thru the drain backs but if it s not all rusty and they did not fill it to the top of the intake with water . look at the cam bearing if not melted out of the block and come out nice and you feel very lucky you could try it .i am not lucky so i wound not do it .lifters may have junk in them as well