The labels on the cable is just for knowing which physical position the drive occupies in the system. It's not for SCSI addressing purposes. Most likely there are small jumper blocks on the drive itself. You will probably have to get the drive brand and model number and do a Google search for the technical specs to find out about jumper settings. Some have them on the label but too often they are not or are unreadable. You need to pay attention to things like if it's single-ended (SE) or low-voltage differential ( most newer drives with 68-pins are but not all) (LVD) and if there are jumper settings to configure the drive one way or another. You would want SE for the VAX SCSI controllers. There might be other jumper terminals for termination, unit enable and other options.
I assume the 68-50 pin adapter looks something like this
https://www.ebay.com/itm/315071353208