with the help of a friend, she found this from the 1999 USAC rulebook
1O4 Dead Heats (c). "In road races, should two or more riders make a dead heat for first place only, they shall reride the final sprint for 1,000 meters on road bicycles to determine the winner. If the dead heat is for any other place, the riders concerned shall be declared equal and the prizes for those places shall be added and equally divided or duplicated at the discretion of the organizer."
The UCI rule was very similar.
So at least for the period this rule was in effect there should not have been ties for first place. there are other rules about splitting ties in stage races, MTB, CX etc.