I haven't looked at the dent pictures but, along the same lines as the paintless dent method, you might build a jig or straps to retain the form of the good parts of the tank, and use air pressure to blow out the dented portion. 

 Harbor Freight has a cross-bar dent puller. It uses glue to attach to the panel. One user reports successfully pulling dents out of a motorcycle tank. Success seems to depend on prep. 70 reviews, three stars. For $11.99 it's worth a try.

 This got me wondering if one couldn't do something similar with a large flat-head screw or nail. Glue it on and use a slide hammer. I don't know what adhesive i would use but there are many to choose from.

 Should you choose to weld studs on the tank, drop some dry ice into it first. When co2 vapor comes out of it, you're good to go.

Mark

That is a great tip on the dry ice. Simple, I love it

I wear a full SCBA mask and do all my welding in an inert argon atmosphere chamber....

Seriously though, good tip!

On another note, I tried "drifting" the spindle out with Thor this afternoon. No go. Thought I'd simplify a bit and took the sawzall to the joints an separated the control arm from the spindle. After that, the ends of the spindle pin literally dropped out of the control arm!... Sadly, the spindle centre section is totally seized. I gave it a few whacks and realized this will take heat and pressure...

Back at it tonight with a torch and heat gun followed by Thor. If that fails, off to work it all goes to the 50 tonne press!

I haven't looked at the dent pictures but, along the same lines as the paintless dent method, you might build a jig or straps to retain the form of the good parts of the tank, and use air pressure to blow out the dented portion. 

When I was a kid, we could perfectly straighten out a dented up beer can by exploding a firecracker inside it. Maybe a cherry bomb might do the trick on the gas tank? Remember to drain it first! 

Hmm I don't have any cherry bombs... Let me look around work and see what I can find!

I'll check with the boys in bomb disposal this morning

 Golly. I never realized how simple it could be to remove dents from a tank. Step 1-remove tank, just in case something goes wrong, Step 2- do not clean, put a fuse in it (just to be safe), Step 3- ignite said fuse, VOILA, a straight tank or shrapnel, Step 4- paint the tank, if there is anything left of you or the tank, Step 5 reinstall the tank. WARNING steps 4 & 5 depend greatly on your & the tanks survival.

 Seems simple. What could possibly go wrong, go wrong, go wrong, go wrong, go wrong

 Harbor Freight has a cross-bar dent puller. It uses glue to attach to the panel. One user reports successfully pulling dents out of a motorcycle tank. Success seems to depend on prep. 70 reviews, three stars. For $11.99 it's worth a try.

 This got me wondering if one couldn't do something similar with a large flat-head screw or nail. Glue it on and use a slide hammer. I don't know what adhesive i would use but there are many to choose from.

 Should you choose to weld studs on the tank, drop some dry ice into it first. When co2 vapor comes out of it, you're good to go.

 

Brilliant!  When I welded on my tank, I purged it with shielding gas from my MIG.

The offending seized spindle pin section...

We will see how he likes my little friend!

Be careful you don't break anything you'll need later!

That's a BFP. Something's gotta give. How about a video.