<< but sometimes a little judicious heating with a propane torch will
pave the way for the vice grip to work. If I was going to try a torch I
would be extremely careful using it, possibly making a metal
shield/blocking device to keep the flame or heat from going anywhere but
to the flange the exhaust studs fit into.>>

And here is the problem.
A propane Home Depot propane torch isn't going to give you enough
concentrated heat as the stud boss in the head to even budge the frozen
stud.

Not in any proficient manner anyway.

The flame is to cold, and much to broad to pin point enough heat to
budge the bolts, studs nuts, or the studs themselves.

I just dropped my exhaust system in 20 minutes using a oxy acetylene
torch.
If the nuts or bolts even looked bad I heated them up white hot and they
popped right out.

When I had the heads off the engine I heated up the stud bosses with the
small brazing tip and they all came out immediately using a cocave jawed
Vice Grips

If you have a bunch of time, and aren't concerned where the heat is
going use the colder propane removal process.
It'll take you hours instead of minutes, and more than likely melt every
wire, hose, or whatever that's within close proximity to the area your
heating.

Use the right tool for the right job.