The transfer case switch is not hard to do---unless the front body mounts are rotted off ( under the front door hinge area) then you have to jack the body up a bit so your hand fits to remove/install the switch. BTDT
Usually the switch ruptures it's diaphragm and sucks ATF into the vacuum system actuation motors, as well as the manual dash switch.
so you get to replace them also.
Have you had to remove the dash yet to change the heater core?
oh what fun
Did I mention the rotted out front upper control arms?
it happens in the rust belt part of the country all too often.
Ya, I do like blazers.