Uhuh...
Procurement was different in the 1960's: Sole source studies, then RFPs.
These "studies" in the 1960's were very real and serious engineering studies, undertaken with the view of real hardware to follow. As for the cancellation of the manned Mars program, it proceeded from the return of the Mariner IV images in mid 1965 on to 1972.
At that time it was hoped that the shuttle would reduce launch costs enough to once again make manned Mars flight "worth it"....
bye,
ep