Ray, You sure they are SBP? Surfin around and consensus is they were never available from factory and neither was 15" on a 66 Belve....
But we all know Mopar was known to do WTFTP for special order. Did find a post of someone having centers swapped to make a set.
like the 1971 Scamp 340 I saw - special order by an executive.. true 340 car, rallye wheels, hood stripe kit, sharktooth grill - - the whole 9.. God I wish I had gotten that car...