Interior Access Panel to Sending Unit in 70 Duster?

Don't cut an access, just, don't do that. Mega Parts, Vans, Year One, Classic, several places for a wrench, their about $15.
First off, you know that all of the new senders are junk and incompatible with your fuel gauge, right? Is the orginal sender still in there? Why do you want to pull the sender, is the gasket leaking?
I have always dropped my tank out, hell, it's out right now, but I think it's possible to pull the sender out without removing the tank.
Kim mentioned this already.