If you've got alot of time, you can do what my son and I did to my '71. It started with no leg room and I swapped in a TH350 tranny so he decided to move the rear axel back 4". We cut the spring purches off and re welded them back to the end of the frame.
Next came the tub, he cut 4" out of the side of the tub rear where the corner starts and cut in front of the wheel well and removed the side of the tub. Next, we moved the side back to meet the rear of the tub and started welding it back on (save the 4" piece for a fill in on the top rail ahead of the wheel well). All that's left on the side is to fill in sheet metal ahead of the well near the door.
The inside wheel tubs were shortened 4" and welded back together next giving me all the leg room I need. It came out great, with a little filler, you won't be able to tell, just wonder what's different!