Rob,
Yes the heat shield can be installed with out removing the exhaust, but it would be better to unhook the rubber donuts holding the system in place and let it hang down. Have someone hold it so it doesnt drop too far and crack the manifold. Then a small phillips screwdriver a 3 phillips metal screws with blunt tips is used. These are about 1/4" long with the wide threads. No longer, or if you are a stickler for foot pain, they will stick out from the floor inside.
Hope this helps.
Walter
1967 220SL-diesel-all heat shields in place.