I've only done the pillars with the bulkhead off the car as we were rebuilding the whole thing. Like that we could get around it with a grinder and welder easier than in situ anyway. ours should have been replaced really but its all good now and nigh on perfect!
We just cut out the bits we didn't want and patched the new ones in. Everything is good and straight. I like to think most things are repairable given the time and patience, and new ones can be pretty pricey!
We also did the feet of the pillars where they bolt to the chassis, but the parts we ordered weren't genuine so the they were about an inch too tall (had the holes for the hinges in them already) so none of the body fitted correctly afterwards. its a pain in the arse when you go to fit the wings and rad after putting all the engine and wiring in, only to realise the bulkhead is at fault!