Most of my bikes are 90 degree stems since I tend to prefer a smaller frame. Personally, I would not go any more than 90/0 degree on something as racy as a Merckx. Finding a 90 stem with 26.0 clamp is a constant quest for me. Nitto Dynamic II has the most classic quill look but not sure I’ve seen it with a longer extension than 110. Salsa, Ritchey and Sameness are also regular searches for me.

Below is my Tempo with a 90 degree Ritchey and 130 extension. A Dynamic II would be a better aesthetic but I needed the reach. If you think you need even more height, maybe a long-quilled Technomic is a better route.