You need the dash partially out.Let your steering wheel rest on the seat,unbolt dash behind left and right kickpanels as well as screws at base of windshield by defog vents.Lower centreduct and any other obvious hardware.You should be able to pull the dash out and brace it with a piece of wood or something on the passenger side(You want the dash out as far as possible on the passenger side,drivers side can sit wherever it wants to sit).Unbolt the heater box from the firewall from under the hood(screws behind computer and A/C accumulator on pass side as well as behind breather)Remove hoses and from under the dash,pull the box towards you and down(don't take it completely out.You should be able to get the screws that hold the core in place by reaching over the pulled out dash.There's a bracket and a ground strap that hold the core tubes in place.This needs to be reinstalled properly or it will prematurely fail.
It's far from the worst I've seen but anyone who says it is easy has never done one.Just go slow,be prepared to wiggle things a bit but if things aren't moving,find out why.Which reminds me,before you drop the bolts for your steering column,gently disconnect the cable that runs from your shift to your prndl or you'll break it when you drop the column.Disconnect your battery before you start as well so you don't fire you air bag.