Glad it's done. Not looking forward to that. I tackled half the battle a few weeks ago doing the exhaust bracket. i encountered the same problems getting a grinder on to the back 2 studs. Spent 8 hours over 2 days to get 2 bloody studs out. Lots of fluid, grinding with a rotary tool with limited access, hammering and swearing. I didn't need to actually replace anything other than the bolts, so wanted to sort it now ahead of any other jobs that I may need to do in future.
Anyway. Congrats on a job well done and for persisting.