Ok I swapped the speakers out, I can confirm that in a 2011 D22 (which only has front speakers) has 6.5" Clarion 40w. They sit in a nice little plastic mould that holds the Alpine type-s 6.5" perfectly with no mucking around. Pulling door panels of the Navara is hella easy to, same as my old Silvia, couple screws and clips and u beauty!
Nissan also have plugs on the end of the speaker wire and the speaker, which make life very easy, u can unplug the stock speaker, rip the plug off it, solder the new speaker wire to it and then plug her in, which means u can install new front speakers without touch any of the cars wiring.
The sound improvement is pretty good for a set of $110 speakers from JB, should hold me for a while until I do the hardcore upgrade.