Bout the only way to get it off is to unbolt it from the front. Sometimes it's best to pull the whole heater box as you can have all sorts of crud around the heater coil it's self. I believe you can pull the heater blower motor without major removals or to make it easy, support the hood and remove the hood hinge from the fender on the pass side. that makes taking the blower out very easy. If you want to pull the heater assembly, you may have to pull the inner fender or at least drop it down in the back. You may also find that mice made this their winter quarters and may also have sharpened their teeth on the blower fan by chewing thru some of the blades!!! While at it, stick you hand thru the quarterpanel access flapper holes (both sides) and see if your side boxes are filled with leaves and crud. They probalby need cleaning out as well--sorry but these trucks have some poor design areas and these are two~~~~
Huck