GAS TANK

That to my knowledge is the only way. I just did this a few months ago. Due the the irregular shape of the tank up under the side body panel, it just can't be squeezed out. It is good however to do lots a simple maintenance while the engine is out and look for other signs of rust. My tank rusted just under the half support under the tank. There was a rubber strip glued to the tank and water had been captured under that spot. What was first a pin hole changed to a thumb hole when I applied pressure to the rusted point. There are several options on replacement tanks that range from the hundreds of dollars to the thousands, so understand your current and future use and budget. Remeber to change the hoses while you are there, it will save you time and grief in the long run.

I also just completed the gas tank refurb and am sure the only way to get it out is to remove the engine. Unfortunately, no way around it (good time to get the ZF checked out!). The POR-15 people have a kit to recoat the inside and in the instructions they discuss a method to seal holes from the outside. Also Jack has discussed the use of bondo to seal holes. In the past, I have found that where there is enough rust to eat through the metal there are larger issues you can't see.

The engine must come out, or you remove the left quarter panel. And while the engine and transaxle is out, you can do the following (what I call 'winter projects'):
#1- clean out the area behind the gas tank. It accumulates sand & dirt which holds water and we all know what THAT leads to.... A good shot of Rustoleum or POR-15 after cleaning will preserve the area for a decade or more.
#2- flip the ZF upside down (after plugging the breather tube), remove the bottom plate and check for the presence of safety-wire on the ring gear bolts. There are 10; be sure all of yours are still intact. The vendors have kits to do this, with instructions. Torquing the bolts (to 65-70 ft-lbs) is done with a crows-foot socket from Sears- basically an open-end wrench thats a socket for a torque wrench. The wrench size will depend on who's bolts you get. If you go slow 'n easy, the bottom cover will come off with the gasket intact. There are shim-washers at each end of the two long bolts; keep track of them 'cause they must go back, or you could crack the iron axle-plates on the sides during re-tightening.
#3- replace the (probably rotted) foam rubber the gas tank sits on. This stuff soaks up water and then holds it against the tank. Most tanks were unpainted and some have rusted through from the outside-in. The hold-down strap has the same stuff glued to it. Replace both with sheet rubber- old inner tubes are better than whats there as-stock. Lots of guys epoxy-paint the tank before returning the components to their places.
#4- replace ALL visible rubber fuel hoses., even the mmetal-braid covered ones up on top. This stuff is getting old, brittle and will someday crack, siphoning all your gas onto the ground (if you're luck) or onto the hot headers (if you're not).
Then go drive your better-than-new Pantera!