The Saturn V-C, was just like the Saturn V-B, studied in the same year as the V-C, except it would use a S-IVB second stage to get a payload into a higher orbit. A Centaur third stage was optional for deep space missions.

References

Lowther, Scott, Saturn: Development, Details, Derivatives and Descendants, Work in progress. Available chapters may be ordered directly from Scott Lowther at web site indicated. Accessed at: https://saemobilus.sae.org/content/680358

v t e Saturn launch vehicle family
Early proposals	Juno V Saturn A-1 A-2 B-1
"C" series	Saturn C-1 C-2 C-3 C-4 C-5 C-5N C-8
Saturn I series	Saturn I IB IB-CE IB-A IB-B IB-C IB-D INT-05 INT-11 INT-12 INT-13 INT-14 INT-15 INT-16 INT-27 LCB
Saturn II series	Saturn II INT-17 INT-18 INT-19
Saturn V series	Saturn V MLV V ELV INT-20 INT-21 INT-23 INT-24 INT-25 Saturn-Shuttle Saturn V-3 V-A V-B V-C V-D V-Centaur Jarvis