how hard is it to replace the heater core on a 1985 dodge d350 with ac.. on 1990 Dodge D350

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is it something that can easily be done at home
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shows about 3 hours to change. in case under passenger side dash. case has to come out. have to evac a/c/
so if the truck used to have air but no longer does and wont, is it the same time.... is it pretty easy to get to ??? is it the same heater core or can you use the one that is actually for truck without factory air..

thanks, jimmy
don't know difference in heater cores. case still has to come out to replace, just don't have to bother with a/c.