Anybody change the thermostats on a 8.3 A2 engine?

[1 Patriot-of-many]

My M936A2 wrecker is overheating, I thought it would be the shutterstat, but the cross over pipe it mounts to and the radiator don't get hot at all while the engine is overheating. It looks like a night mare to change those two thermostats! Anybody change them out and any pointers before I decide to either shop this out or follow the TM's and tear this stuff apart? EDIT: Looks like I have the external bypass, with one larger thermostat.