Heater Core Replacement with A/C??

[texjake]

I am sure this has been covered 1000 times on here & I have found some post on here about changing out the heater core. But most are about without A/C. What I want to know is; are they all similar to the fact that you have to remove it from the engine side & that you have to remove the inner fender well on the passenger side to get to the bolts or bolt? Also, are they all basically the same across the board as far as year models are concerned? Like is the A/C heater core box the same for a 68' model as is it for a 71' or 72' model? Because mine is a 1968 with A/C. I have already started deconstruction on the interior dash of my truck and can see the heater core from inside the cab & the bolts on the inside attached to the firewall. Any help on this matter will be of great assistance to me, Thanks!