I.P.S.
Welcome to the N.I.A. Forum!
The 1969 SS 427 Impala is the most difficult to certify of all the Impalas. It is also the easiest to clone. The VIN # nor the Cowl Tag reveal any clues as to SS option in 1969. If you were reasearching the 67-68 model years, you would be looking for RPO code 4-D on the cowl tag.
This link may be of some help with your search.
www.impalass427.com/1969_SS427.htm
The best tools to identify the SS optioned car are the POP and/or Build sheet.
Remember that in 1969 the SS Impala was a 427/390hp ONLY option. Since the SS 427 was slated for removal from GM's performance line-up, only 2455 were built.
Hope any of this information helps you in your quest to certify you car. While I am NOT anyone's expert on the 1969 Impala SS, I do own one and know just slightly more than a Stop Sign. If I can help, just ask. (I do know people that know way more than I do!)
BIGIRON