Gray cast iron will work just fine for you. I have used it and it worked great and machines very well. There is also ductile cast iron it acts more like cold roll steel and can be heat treated to about 60 rockwell C. I have not been by the fame site for some time now and see not much going on. What happened to everybody???? It use to be a very active place with lots of good members. Anyway, I hope this info helps you out. Good luck with your build.
Hi Craig, I use a lot of sash weight cast iron in my model making, and it makes supreme liners, mainly because it is usually well over a century old, and has had time to get the grain into a perfect state for machining and finishing, it comes up like slightly dull chrome plate. Unfortunately, with myself being from the UK, where good quality sash weights were made, other friends who live in the US haven't been as lucky, finding the sash weights very badly chilled, and almost impossible to get the outer 'skin' off. For what you require, almost any of the good quality continuously cast cast iron will do, and in fact, if you are lucky, you can find the same thing in very thick walled tubing, so taking a lot of the hard work out of the boring process. If you are making a cylinder for an i/c engine with piston rings, then really you don't need a perfect finish, it will need to be honed and then the piston and cylinder are run in together to make sure that mate perfectly (running in together over a period of a few hours). If making any other sort of bore, requiring a very good finish, then lapping will be required. You are very lucky in the US, adjustable copper laps are very cheap to buy in the correct sizes that you require, and should give you a nice perfect parallel bore.