Okay so you have a vision of what your truck can look like. Thats great.

Im guessing that you want 4wd as in SUV/truck type and sitting high with big wheels all round. And not a canyon burner with a car based 4wd system (tho that would be pretty cool)

Then I would suggest you get the chassis specs of your truck - wheelbase, track width etc and figuring that a chassis swap will be easier than fitting all the 4wd stuff to your old chassis, start comparing it to whats out there.

Buying a complete wreck will be much cheaper than buying the bits one at a time.