I have a 1990 2wd Project truck. I am trying to find out ifis is at all possible to make it into a 4wd truck. and how i would do this, if it is possible.  

Anything is possible with enough time and money but given that resale value of 4x4 trucks are at a all time low because of gas prices I would suggest you get a truck with 4x4 already. You would be ahead of the game time and money wise.  

IIRC -A cab and bed swap is easier than swapping the parts on the 2WD chassis, but IDK for sure. But it is very doable either way.  

Its very easy and has been many times.  If I were doing it, I would find a 78-79 Ford Dana 44 in a junk yard and take everything - hub to hub, radius arms, etc. They are super common.  I would take the spring buckets from the frame.  I'd contact a local Ford parts counter and order pre-superduty front shock towers.  Then I'd use Bronco Grave  Yard's Deaver springs (select ride height).  Typically, 6 inches in needed if you use a solid axel, but 4 inches is possible too.  Good sources for parts are Bronco Grave Yard and Cage Offroad.  There are other forum that specialize in this area.  Use Google if necessary.  Contact WFO Concepts for steering components.  Again, sounds tough, but not really.

OR...

You could find an 80-96 Ford 4X4 and swap every suspension part from doner to keeper.  

Dont waste your time sell it and buy one thats already 4x4 unless the truck has some kind of sentimental value and you have more money than sense I would change my direction.