In issue 24 (August 1999) of "Oracel Update" magazine (Xephon plc) I published an article "Moving Optimizer statistics between databases (Oracle 7.3)" that deals with this problem, long time before Oracle introduced DBMS_STATS package.

Since the article is more than 2 years old you can download it for free (along with the accompaniying SQL/PLSQL code) from Xephon's site: http://www.xephon.com/oracleupdate.html

On the bottom of the right side of the page click on "Other issues" and then find August 1999 issue. You will have to register (it is free), then the whole issue (PDF format) will be mailed to you. You can view the code online by clicking at the title of the article.