Welcome Fladdra......
Typically you have to remove the dash completely to pull the heater core out of the truck.
What are the problems that you are experiencing? Is it that you just aren't getting any heat out of it? Or is it leaking coolant into the cabin?
If your just not getting any heat, then check the cable that moves the shut-off valve near the gas pedal of the truck (Left hand drive trucks!). Just turn the dash knob from cold to hot a few times while looking below the dash close to where the gas pedal is located.......kind of above it and right over the transmission hump.
BTW, you DO NOT have to remove the dash to check the temperature cable functions.
Here's a pic of the valve and lever that the cable controls......