Mr.Polecat,
Leave any reaming to a gunsmith( I recommend no reaming),but you should be able to make a chamber cast yourself. A .308" bullet should drop easily in a fired 30-30 case, if it won't, something is wrong. The old 30-30 chambers are usually pretty generous anyway. Slug the bore, a 30-30 will be around .308", a 32 Win.Spec. .321-.322".
Mike