Once I track down a W115 I can figure out the best place to splice the two -- I think you're 100% correct. As for the stop, are you talking about the pushrod? The push rod travel is limited to around 3+". It's definintely not 4". The MC has a "tube" in which the push rod end enters. Around 1/2" of the pushrod permantently rests in this tube. On the W123, if you fully depress the brake pedal arm, it will eventually hit the assembly housing. However, the rod does not go more than 4". Is that what you mean by a stop?