I finally started the project. All of the original vinyl tubing has been removed except for the hose connected to the starboard tank. Underneath the nav station, in the original battery compartment, there is a ~4" access hole. I can see the hose to tank connection through the hole but it's not accessible. It's also not accessible from below the quarter berth/under the nav station. My plan is to cut some of the plywood/fiberglass that holds the tank in place and lift the tank out from under the settee, attach the PEX and reinstall.
Almost all the other PEX line has been ran, no connections made yet. I'll try to post some pictures.