Quick Heater Core Replacement Question

[Bob Q]

I'm about to tackle a heater core replacement job on an '84 K2500 with A/C. This truck is fairly unmolested and still has all of the factory insulation around the A/C box under the hood and on the firewall. Are there any bolts or nuts that are behind the factory insulation that I need to remove to get the heater core out? I was wondering if I was going to have to cut out and remove that factory insulation, which I'm hoping I don't have to.

Thanks.