Well, let's put it this way: of the 2 jobs, I'd rather change the head gaskets. Yeah, getting to the heater is a HUGE PITA on these trucks.The entire dash is in the way. Plus, the section with the AC evap coil needs to come out first, so you're really supposed to discharge the AC first. Folks do it without doing this step, but it's a huge pain.
Hope you got a warm garage to work in, and lots of room to lay out the interior parts. Get some old muffin tins or egg cartons to keep the screws and bolts organized. Pull the seats out first so you have plenty of room to move around. Good luck.