I needed to make a t-slot nut off-center to adapt a metric pillowblock with 42mm hole spacing to English 1530 80/20 aluminum extrusion with 1.5" t-slot spacing (38.1mm). I also wanted to change the nut holder profile a bit to make it better fit the extrusions I had. The source object was used as a reference but I wrote the .scad file from scratch (for better or worse). The nuts I used were #6 and #10 SAE Nyloc nuts but the dimensions can be changed easily. The nut width specified in the .scad file is for the largest width of the nut.
I uploaded an experimental version for 1010 series aluminum profiles but have none to test on. There wasn't any wiggle room with #6 hardware so I sized the .stl for #4 hardware but again have no way of testing the nut on the aluminum so I'm not printing it out... you'll probably have to play with the dimensions.