You can safely clean it with a piece of scotchbrite pad and spary carb cleaner,or brake clean,or laquer thinner,gasoline,kerosenne etc.etc.
That being said I see over and over guy's making the big mistake that you are fixing to make, a high milage engine that now has the compression bumped up with fresh heads and a lumpy cam, a sure invitation to ring blow by and oil burning. For $337 bucks you can get a complete quality engine kit from these guy's http://www.rpmmachine.com/index.html, spend another 400 to 500 bucks at a local reputable machine shop. Then you and the kid can spend a few nights or weekends in the garage assembling a fresh engine. Theres hundreds of how to books and videos out there on small block chevys so do some homework,have some fun building it,and I gaurantee you'll be a lot happier.