Vintage HP 456A current probe/clamp battery replacements.

Hey guys. I inherited this wonderful little HP 456A current clamp a while back and I have been trying to find batteries for it with no avail. I have looked at the manual which states that it requires TWO TR 233, and ONE TR 234 Mallory mercury (stable discharge voltage) batteries. the problem is I don't know anything else about these batteries. I have found that the TR233's are supposedly 4-4.2 Volts, and the TR234 is supposedly 5.33 Volts. Now my plan is to use 2 or 3 18650 or 26650 batteries in series and two separate voltage regulator to supply individual voltages, however I still don't know which of these battery holders takes what. In other words I don't want to assume that the larger battery holder takes two batteries in series and the smaller takes the single battery. Since I have no actual information on the battery sizes it is impossible for me to know for sure. My guess is that the smaller holder takes the single TR234 and the larger takes the series set of TR233's...? does anybody here have any ideas or advice?
I've attached pictures for reference. I decided to post here as this old conversation is one of the older ones regarding vintage gear per this forum.
Thanks