As anyone who has used an X2 minimill knows, y-axis travel is very limited. I converted a minimill to cnc a few years back and have been constantly plagued by the lack of y-axis travel. Push came to shove when I wanted to use it to machine parts for a gantry router I have under construction so I finally decided to do something about it.
On his website, Hoss lists a couple of mods to the y-axis to extend it around .75" in one direction and around 1.5" in the other. Unfortunately, the latter allows the saddle to over travel the ways by an excessive amount. This thread describes how I solved that problem by extending the y-axis ways.
I began by hogging out the throat of the minimill base. This modification encompasses Hoss's modification and the modification which can be found in the Y! minimill group. This modification necessitates relocating the column mount to the back of the mill base. Shown in the first few images are the throat clearance and the initial milling of the flats for the new column mount.