Depends what wheels you wanna run, why not HQ stubs, gotta be a bit careful with torana ones, it affects geometry and they might be hard to get down there. You will need to keep the HR stub axles, as Torana have the wrong inclination, and will not allow you to set up the front end geometry correctly (castor and camber will be affected, making front tyres chatter on turn probably).
HQ or later discs (up to WB) can also be used, allowing for a change to the later Holden. But depends on what ya want to do with the rears. It's quite cheap and easy to do a shortened borg warner diff at the back, either drum or disc. Again you have some thinking to do while its being re bodied
You should have a look at some of the build pages mate, lots of info, or use the search function and type in "sub axles". It really depends how far you gotta go, I dont see the point paying a blaster to spend hours blasting stuff you wont keep, like outer sills, when the inner sills are not exposed, the floor when its gunna be completely replaced etc etc... Ask your fabricator dude if they can cut the outer sills off if they are knackered, get it to bracing stage and all bits off, then see if they can get a mobile guy to come into where its being worked on and only blast what needs it. I'd personally do as many flat or accessible panels with a large polishing type sanding disk, 80 grit or lower and get hard areas blasted, but all depends how much u wanna do yourself.
But you will get differing opinions, but its a lot of wasted money on painting areas that are gunna be scrapped. It also depends if you wanna do a rotisserie job or roller.