Hello all,
After having some difficulty attempting to remove my '81 300D's cruise control amp, thought I'd share a photo with you of what to remove. Note that it is a tight area to get into; use a 10mm socket with an extension to remove the bolt in the photo with the red arrow pointing at it. On first glance, it doesn't appear that a socket/wrench/extension will get underneath the brake pedal in the rear area, but it will. See also the video in the link below (in German---start at the 1:00 mark) that shows how to do so. Should alleviate a lot of swearing on your part to get it out; I suffered for a couple of hours the other day before I found this video.
https://www.youtube.com/watch?v=YJdxSlgSBlU