Bought a 63 tank from AMD on a closeout sale. I wondered if the 63 model would work in a 64-44 with a different suffix on the part number. Well, I can tell you its a big YES! When I dropped my 65 tank, I found the same looking flange gasket that was stuck on the 63 tank from AMD. I measured the ID and they were both the same as the filler pipes didnt change from 63 to 64 in a Valiant. The gasket it self is slightly different as the AMD 63 gasket had a larger lip inside but it was the same other than that small detail.
So onto the tank removal!
First thing you need to do is make sure there is little to no fuel in the tank, this will make it light enough to maneuver out of the car.
Drop the cargo divider so you can manipulate the fill pipe from within the cabin. Remove the sender electrical lead and the fuel line from the sender.
Next you need to remove the fuel pipe vent line right behind the filler flange, it should pry off with a screwdriver if you cant just pull the rock hard line off after the next step.
Remove the 3 screws of the filler pipe flange under the fuel cap. now you can get a screwdriver onto the rubber vent line and pry off the nipple. I had to replace that piece with a new one.
Now you can push the filler pipe into the tank about an inch and then rotate it 90 degrees. You want to get the filler pipe as far out of the tank grommet as possible before you drop the tank.
Now you can loosen the strap on the passenger side and lower the empty tank, it will weigh about 15 lbs now. Keep working the tank off the flange gasket and it will eventually come apart. drag old tank out and clean it or replace it.
Put gasket into tank flange and grease filler pipe.
Install sender unit and make sure the lock ring is seated in the 3 lugs.
Remove jute insulator from old tank if its still there and glue to new tank top. Once again, rotate the filler pipe to a position that will allow the least amount of filler pipe to be showing under the car, I got it up into the fender with the flange pointing back so there was about 3" showing under the car and to a position that was pointing down and as far forward as possible. This allowed me to just hook the greased filler pipe into the flange and wrestle the tank up into mounting position and hook the frame with the strap and fully unscrewed tensioner. If the filler pipe is not separated from the fender fill location, the fill pipe is too long under the car to fit the tank flange as the tank cant get into that position due to the spare tire well. Now you can grab the filler pipe and twist and push into mounting position and screw the 3 screws in.
Once that is secure you can push the vent tube back onto the filler pipe and don't forget the little anti-rattle clip that secures the vent tube to the chassis.
Finish off by tightening the strap nut and attaching the fuel line and sender lead. I have found that you do not need to remove the 5 screws under the rear cargo deck gasket during R&R nor purchase the more expensive 64 style tank if you use the 63 gasket on the 63 tank as I believe the gasket design changed in 64 only, both used the same filler pipe but I was unable to see any difference in either tank when placed next to each other minus one small dent top center behind differential.