I don't have a Littman and have never seen one, but I do have a conversion (combination of a 900/800/110a) with a Sinar back and a Schneider lens that I built myself. It is difficult to beat the negative size, that is for sure. I have built three, the last one for a friend (I swore I wouldn't do another after that due to the time it takes), but if I ever get my hands on the Xenotar like you have, I will make one with that. A lot of people complain about the rangefinder going out of alignment, but I have never had a problem with mine. It has been going strong since about 2007. I really like it for shooting Polaroids and people, though I don't do much of either. It is very easy to handhold I have found. I just rest it on my shoulder.

Here is the camera-

Here is an image from it handheld-