I just completed Aux tank installation on my 1997 Voyager
Tank: OEM tank from Florida Marine Tanks - should come with sending unit pre-installed
Parts:
-Grady Parts List:
-2nd filler/cap assembly or match existing with after market filler (Grady model has vent hose connect fitting - Match Aux to Main Tank Filler)
-Fuel Tank Three-Way Valve Brass 3/8in and Brass barb to NPT fittings - Moller Marine is good one
-Double-Throw Grady fuel tank select switch to switch fuel gauge readout from aux and main tanks - may need to go aftermarket given your 1985 model year.
-Other Parts:
-Aux Tank Filler hose with double hose clamps installed at each end (Shield Marine Hose) - hose may already be factory installed as mine was)
-New Marine fuel line with double hose clamps at each end - Replace main tanks lines while at it (Shields Marine Hose)
-2nd inlet fitting to your water/fuel separator for aux tank fuel feed line connect
-Rubber Matt for new tank to sit on
-Tank mount spacers and/or hold-downs (Starboard, HDPE (PVC) Plastic Board, or Hardwood) see below video and your main tank hold-downs for ideas.
Good watch for new fuel tank installation:
Couple of pics from my Aux install