GG's-

I've finished with oil, I've finished with shellac, but this is the first time I
'm 
going to finish with shellac over oil.  Do I need to do anything to the final 
oil coat prior to the first shellac coat?  Lightly scuff sand w/400+?  
Burnish with an old rag?  Lightly scrape with a toothing blade in a 112? 
(Awesome scraping plane that I'm joking about using, Jeff.)  The only 
two things I'm concerned about are the finished looks of the piece ( a 
large bookcase) and the adhesion of the shellac to the oil.

Any input is appreciated.  Thanks.

-Brent Clukey