If you are sticking with the ODB1 then there is nothing to upgrade electrical. There are differences between the 5.2 and the 5.9. The Flywheel and Balancer is not the same make sure you have the one for the 5.9. Also, differences in stuff like the alternator and some of the pulleys. Keep the 5.2 around for parts until you get the 5.9 in and running.
If you are planning on upgrading to ODB2 then it's a big job it would be easier to buy an entire truck, there is so much difference.
A hemi upgrade using ODB1 would be difficult non of the sensors will fit at this point I would go to a carb set up