The results from yesterdays parts trip was I did not purchase the unit. The unit I looked at came from 1969 Dodge Super Bee. Width was from drum to drum was measured with steel straight edge and a new steel tape. The drums were pushed up tight but without lugs and it was 60 1/2". More than the advertised 60 1/8", and even if the drums were on tight with lungs it was far more than the 58 1/2" I'm now using.
My next trip will be to check out a 1965 unit. Thanks to all for providing additoinal information.
Nick Tiberio
FuryUs63