If you want to do the panel beating yourself then stick to the dents, rust removal (if there is any) and paint. I personally wouldn't even consider hiring and using a Porta-Power without being confident in it's use - these can be lethal in the wrong hands.
If you suspect that the rear end is twisted, how do the gaps around the rear doors look? - this is another give away. My ESP (also a 1980 model) has a slightly twisted rear end due to the fact I had a trailer Jack-Knife into the right rear. I took it to a panel beater and he noticed it straight away - the rear right door had nice even gaps at the bottom but got smaller towards the top of the door. Only solution (he said) was put it on the rack and get it back into shape. It would only be a couple of hours and around 2-300 dollars.
Give me some details of your machine, have you got any pikkies - I've owned mine for just on 20 years now, it's a Falcon ESP (not Ghia) 250 4 spd and it's about to get a rebuild.
476 EF XR6 Wagons - 198 were Manual
Member Tickford / FPV Club - SA