It
should work to convert from auto to manual if your year was offered with the two options. I'd consider it highly unlikely that the systems beyond the controls would be considerably different since it's cheaper to make one design and swap out the one piece to accommodate different trim levels. Manual to auto would be cost and effort prohibitive, however, since there's a number of extra sensors and such needed for the auto system.
I was surfing eBay to try to find some manual controls I could look at and came across this. It has the pigtails included, which should make your job a lot easier. If you have gray interior, you could always grab that one for now and keep an eye out for a gray frame for cheap later.
http://www.ebay.com/itm/03-04-NISSAN-PA ... 3m&vxp=mtr
Regardless, you're going to need to pull the FSM up and start studying the pinout diagrams of the nav/non-nav controls to get an idea of which wire needs to be connected to which. I linked to the cheat sheet in the primary conversion thread that I used when doing mine that may help you.