Can I put BBP drums on my 69 ?

They did come with front drums after 72.
Four wheel drum brakes were available right thru the 76 model year production on cars built December 31st 1975 or before.
As of Jan 1 1976 front discs were federally mandated.
All A body cars with 4 wheel drums were small bolt pattern.
All disc brake cars built for the 73-76 model years were large bolt pattern.
The 1973-76 7.25 axles were available in both bolt patterns, 8.25 was large bolt pattern only.

IMO its not worth the extra effort to convert to large bolt pattern drums. I'd just go with the large bolt pattern disc swap. Much simpler. Much, much simpler.