There's not much difference between clean cast and dirty aluminum where I'm at (NC). A month ago there was a 4 cent difference $0.34 versus $0.31. There's a lot of motors out there that don't have a steel sleeve. I used to bore these out, put a new piston and rings in, and it's almost as good as new. don't forget about the cast iron valve seats. These can usually be pried up and out with the edge of a large round punch.