GM-GMC: 1984 GMC 6.2L Diesel Heater core, diesel heater, heater core

Question
Where is the heater core located. So far my boyfriend has taken off the entire dash and heater vents and so on and so forth but now we cannot find the core. Is it inside the vehicle or on the outside by the firewall?

Answer
Unfortunately you have not provided me with enough info to give you the location of the heater core.  Is it a truck or a van or a ???  Some are located under the dash, others are located on the firewall and accessed from under the hood.  Follow the hoses would be the best advice I could give.