Re: rear shocks on 164
Sorry to say you've picked (potentially) one of the worst possible jobs on a 164! The bolts are available from the dealers (or were a year or so ago when I did mine)! There is one long one and one short one on each side. Unfortunately, there is a very good chance they are seized and yes, it IS possible to shear the heads off with a good bar. Also a reasonable chance of damaging the threads trying to hammer them out and as if all that wasn't bad enough, you need to get them past the ABS sensors. Depending on the age of your 164, these might be on a seaprate casting or they might be directly into the hub carrier casting.
The only advice I can give is to clean any surface rust off the exposed part of the bolt shank in between the casting lugs with emery cloth or something similar. Otherwise, if you Do get it to start to move, it can often bind up again as the wider part of the bolt (with the surface rust on) tries to get through the casting hole.
I've taken the complete assembly off the car before now and cut the bolt into sections with an air saw and then brifted the bits in the casting out!