1961 Alum 6 cyl, Psh But Auto, won't crank

Since the START switch is the PARK/NEUTRAL shifter position, there's no need for a lock switch there. There is however a vacuum switch on the manifold that interrupts the starter circuit when the engine is running (eg. running, put it in NEUTRAL). Those fail.

Take the tank out and either use a tank cleaner from Eastwood or Hirsch Automotive (I prefer Hirsch) or use brick cleaning acid from the local building supply. Dilute the acid as per cleaning brick, and get a box of baking soda to neutralize it when done. Slosh it around as best you can for a couple minutes. You only need 1-2 gallons of solution in the tank. I let it sit flat (bottom down) for 20-30 minutes, then rotate it, leaning up on each side to get the sides. Not usually much (if any) residue on the top -- might be some light surface rust. Duct tape over the opening. A 2' or so length of chain dropped inside will help loosen any residue. I've used rocks, like 1/2 gold ball size (#57 stone, not pea gravel!) but it's harder to get all back out. You can attach a wire to the chain and tape the wire outside an opening before covering. Follow instructions if you use a Hirsch/Eastwood kit.

Used to be POR-15 also had separate products to seal tanks and other automotive uses.  Hopefully a product made by POR-15 for fuel tanks is what was used

POR-15 did make a product for gas tank lining -- maybe still do. After a bad experience with it that's the last thing I'd use. It's a thicker liner than most. The kit was supposed to do up to a 22 gallon tank, but it didn't quite do a 100% cover inside my 63 Classic wagon tank (same for 63-66, unless you have the three seat wagon). If you don't get good 100% coverage fuel can get BEHIND the lining. Then it starts to come loose, leaving you with a leaking tank with a "balloon" inside that you can't get out. I followed directions as far as cleaning and such, but it's possible it wasn't quite clean enough. The point is that if it fails you're stuck with replacing the tank or cutting the top out and cleaning. I had used Hirsch liner before with excellent results even though it just leaves a paper thin coating. The newer product isn't as good as the old 80s-early 90s self-etching, but it's still good if you use the kit and clean and etch per instructions. EPA mandates made them change the formula and add a step.

I'm glad you did too!! I still like the Hirsch product so much better. Great for a liner to prevent rust, but not so good at filling pinholes if you have any. Anything larger than a pinhole would have to be epoxied or otherwise repaired. I wouldn't weld on a tank in an area that already has pinholes! The Hirsch liner is fuel proof, obviously, so epoxy the holes then line once epoxy cures -- no problems!