LOL the 68 service manual is correct as is the 276/284 stuff that A56 and georgejets posted.
Go look up the part number in a 68 parts book section 9-15-1 IIRC
Then go to the 68 service manual and check the numbers,
then compare those # to a document (race manual) written a few years later that has a history of pimping and trying to sell mopar branded product to mopar folks.
Yeah, they aren't close to the same numbers, yet the smaller cam 268/276 cam was in production from 1968-1973 model years.
I believe, and measured cams that were in sync, with the service manual because those are the numbers service people had to use when diagnosing.