Sadly, I have a lot of experience with this exactly situation. We're not quite as deep into the Salt Belt as PA but still....
Will be removing at least some heat shielding ...
For this part of the task, the most important tool that you need is replacement bolts. Those little heat shield bolts are the absolute worst: they're cheap metal holding other cheap metal together, they're exposed to every sort of rust-inducing element on the road and they do nothing but cycle from one heat extreme to the other. I'd expect that every single one of yours will snap.
So, plan for it. You'll want a decent metal drill bit (or extractor) to remove any remains of the bolts. If you're "lucky", the nut side of the bolt may have rust welded itself to far side of the shield. You can decide whether it's worth trying to salvage its threads or just chisel it off.
I saw something very similar to what I expect you'll see when I removed my turbo heat shield. Every single one of those little bolts snapped on me. My solution: purchase a turbo blanket and toss out the old heat shield material.
if not also the headers from a Subaru Outback.
Header bolts (and studs) should be much more robust (i.e., grade 8 or better). However, their failure mode is much more annoying and / or destructive. My advice is patience: use penetrating oil, vibration and temperature changes (repeating this cycle many times) before you hulk out on the breaker bar. For example, my little electric impact wrench is unlikely to break off a header stud. However, I was able to snap a motor mount bolt in the block with my breaker bar (admittedly after a great deal of effort).
If things go that badly wrong, you will likely need to drill the bolt out of the block (or have access to a shop or kind soul who will take care of that for you) and fill the newly larger hole with a helicoil.
So, the recommended procedure is:
- Return to step 1
- Breaker bar and hope for the best (how did you end up at this step anyway? ;-)