You didn't give us a whole lot to go on, so I flipped open my part id catalog and for 1968: (I listed to auto trans so you can double check your warranty tag: 1=3spd,5=4spd, W=C4, U=C6)
C4
PEB-B1...200CID
PEE-C1...289CID (Floor shifter)
PEE-S.....302CID (Floor shifter)
PEB-B.....200CID
C6...