If it's actually a Chevy and it's a C20, that means it's a coil sprung front and rear two wheel drive. Making that a 4WD will be very hard if not impossible. Best option would be to do a body swap to a newer drivetrain to get what you want. I would suggest 87 or older with a TBI and O/D trans. 88 and newer has the front suspension grafted into the frame which may make locating body mounts a little harder. Just my 2 cents worth,
Scott
