I just finished my winch install on my 07 420, but mine is a 4x4 and from what I understand, the 4x4 and 2x4 are slightly different as far as winch mounting goes. I ended up putting my winch motor on the LEFT side and having the cable spool off the TOP of the winch (after calling Promark to confirm that this was ok) which deviates from the posted instructions.
I also had to grind on my frond grill in multiple places to get the grill to fit back on. Very tight fit. Mine is a 3000lb winch, but is the same physical size as a 2500 lb winch. If you are like me, you will notice that the wiring gets too hot if you route it along the left side (exhaust). Do yourself a favor and save some rework by just routing along the right side. Mine just barely fit without having to extend the cables.
Like I said, yours is a 2x4 so it is different, but some of the principles mentioned may apply to your install.
HOpe this helps.