I am not familiar with your specific vessel,however earlier model Mainships have port and starboard screw off access ports (appx 6"- 8") in the cockpit which give access to screwed cover plates supporting shut-off valves and sending units, Location may be in salon on some models.I would suggest locating removing and retrieving part numbers on existing units along with measurements for duplication. You speak of 1 tank and multiple sending units which suggests 2 stations individually and independent of one another;all of which is speculative on my part. I've found many
"engineers" do not think about logical means for removal and replacement of many parts and systems whether it marine, automotive, agricultural, or structural (power
plants etc.) gotta miss ole school days where fuel tank access went straight to tank
and you could easily have your faithful notched stick to accurately tell what's on board. Good luck whichever path you take.
Big