I'm part of that creepy Carl following. I think it started with my lifelong (uh....) dream of a 128 wagon w/ a 1500, etc. etc....and I've known Carl a long time.
124 Coupes are wonderful BUT have that niche following that makes them sometimes harder to find in the proper condition & price. I am on the verge of a similar 124 Sedan project using a nice 1800 and a Lada 5 speed. I wish Carl had photos of the shifter (or interior in general) on his Sedan, but my understanding is that with either the 124 Sport or the 131 gear box there's a bit of fiddling to do with placing the shifter in a Sedan, neither option requiring any NASA engineering, of course.
This reminds me, I need to get to work on it! I actually the thing w/ its weepy (fluids) 1592 & leaky (drips) auto to work today....i usually feel like I need to bond with a car a little bit before I really get into working on it.