That's a good question about whether what I did functions. The seat does recline and the heater does work. I actually didn't do any welding, but I did drill many holes to attach and mount the hardware using machine screws. Getting the top pivot points attached to the frame is not difficult, but I suggest getting the bottom in first so you can see how the seat pivots. It's critical that the seat back frame is centered
exactly between the two doors since the seat itself is a tight fit.
Since the point for me was to have it recline, I invested a lot of time into taking apart most of the car's interior to run the electrical. The beauty of the W126 (and Mercedes in general) is the provisions exist to add any of the optional features, and doing so is relatively simple. The complication lies in running wires from the front to the back of the car and into the doors.
As I mentioned before, I'm working on documenting what I did since I have not seen this type of conversion usefully documented in one place, and I'll post it when done. My personal email is nosp*
[email protected] (remove the "nosp*am. -I'm avoiding the spambots.)