In my opinion, it would be difficult and time consuming for a newb, but not impossible.
To over simplify:
- With the engine cool, remove the heater hoses from the heater core in the engine compartment and let them drain into a pan.
- In the cab, remove the shelf on the passenger side under the dash, if you have one.
- Remove the climate controls assembly and disconnect any cables needed so you can swing it to left side and lay it on the floor.
- Remove the entire heater case as one unit to the right and down. It will take some effort to get the heater tubes out of the firewall.
- Once you have the heater case out, split the unit in half to get to the heater core.
- Replace the core, and reverse the process to reassemble. Make sure all the little cables for the climate control go back where they came from.