[watahyahknow]

you might be able to get the back in shape youreself with some chains eyelets bolted intoo a big slab of concrete pieces of wood scaffoldingpipe and a big bottle jack .
if you go eazy you might even keep the coating as good as it is now

use the eyelets and the chain to hold the chassis down on the concrete slab/floor at the start of the bend put the jack at the end and start jacking it up , let the jack go down once in a while to measure and start over to bring some heat in and stop the metal from cracking , for the twist you need the scafoldpole with a fork welded on the end that slides over the chassis either use two (one at each side of the twist ) and use some grunt to twist the oposite or use or use one as a big lever .
go little steps and watch out that nothing hits you in any parts that hurt