Not easily. The blocks are the same, the heads are different.
The bolts don't line up quite right, the intake runners are in slightly different spots, and you would have to take the distributor too, which rotates backwards on the 2.9 because of different cam gear cuts.
What exactly is the point of this anyway? And don't say "Because I don't like/trust fuel injection" or "Because FI is some evil government plot to control our lives."
If you have a truck that was originally equipped with a 2.8 that blew up and you have access to a 2.9, it will probably be easier to swap to FI.
But dont yall know when the gubment sets off tha emp's all yur injectamed "computer ran" motors are goinna crap out!!! Who'll be the paranoid skitzofrenik than huh?! I heard they got big machines to change the wahther too!