What I do to get mine out is to unscrew the flat rubber gasket seal on the floor, disconnect the vent tube from the filler tube, unscrew the filler tube from the quarter panel and then twist it out. It will probably come in contact with the inside part of the quarter panel so be careful not to scrape up your paint. Also, a little silicon spray where the filler tube goes in through the grommet in the tank can't hurt and might make it slide in and out easier. We just had to put a new tank in our 70 chally vert and all I can say is the filler tube removal on the charger is cake compared to the chally.

Same for the installation of the tank. Whoever came up with putting the J bolts on the rear of the tank and then putting the rear valence panel on should be dragged through the streets. Much easier set up on the charger to remove the tank.