The proposed Saturn IB-B was to be essentially an uprated Saturn IB using the new MS-IVB-2 upper stage, utilising the HG-3 engine, developed from the S-IVB and an uprated S-IB-A first stage.
References
Saturn IB-B Wikipedia(Text) CC BY-SA
The proposed Saturn IB-B was to be essentially an uprated Saturn IB using the new MS-IVB-2 upper stage, utilising the HG-3 engine, developed from the S-IVB and an uprated S-IB-A first stage.