not only is it possible, but extremely likely your engine has been rebuilt. The .030 stamped on the piston is pretty much proof of that. Yes you can have cylinders different sizes, I wouldn't recommend it, but yes it is possible. You should get a manual, which is available from nearly any of the normal vendors, or you can go to "OLD ONLINE CHEVY MANUALS" nearly all the manuals are available there. It is quite obvious you are new to this, you need to ask lots of questions. Keep in mind this hobby can get pretty expensive, and if you aren't absolutely sure of what you are doing, you can waste a lot of money really quick. I would also recommend that you take the engine out.
Last edited by brokenhead; 08/29/2014 12:08 PM.
