You're making me blush ;) I'm in the UK and purchased the extrusions from Ooznest and as I said I used the old extrusion as a drill jig. Just line up the old and new extrusion accurately, clamp them together and drill through with a 5.1mm twist drill. The screw holes need to be counter bored to accept the M5 screw heads, I just used an 8mm cylindrical burr from the amazon in a power drill. That worked surprisingly well. Then you just need to thread the holes (M5) in the uprights if you didn't have it done by the supplier.
Make on!