I'm not sure if you understand the question correctly, is the yuv converter outputting the 4:3 video in a 4:3 frame or does it stretch the content into a 16:9 frame?
Why would the YUV converter stretch it? If it is it's a piece of junk and should be replaced with an Indivision (haha, yes, my biased opinion), but in any case nearly any good TV has an option to stretch 4:3 to 16:9 or not. It's an option in the menu on the TV. Same thing, if your TV doesn't have that option junk it for a better model. Heh.
