The 124 filter can be very confusing. I believe by 1995 they all had them. I went to the Bosch site, waited quite awhile, and it seemed like it was going to give me a pdf file for instructions, but the instructions never appeared.
You can identify if your 124 has a cabin dust filter by looking at the trim underneath the wiper arm. If there is a hard plastic U shaped ("smile" shaped) piece of trim, with about 5 small phillips head screws holding it down, you do NOT have the dust filter. If this area on the otherhand is a solid piece of rubber, which will pull up out of a channel, it has the dust filter. You can also try looking for the filter through the air intake screen for the climate control, but checking which style molding is under the wiper arm is even easier.
The installation I would say is easy to moderate in difficulty, an experienced tech should be able to do the job in 15 to 30 minutes if nothing goes wrong. The filter is accessed from the underhood area on a 124 chassis, NOT behind the glovebox like on a 210 chassis.