i get to do mine (again)in the next few weekends too because when i did the intake swap i broke the tube coming out of the firewall (the heater core tube) by jolting it around too much
you do NOT even have to touch the AC system
when you get the dash off, just take a dremel with a cutoff wheel and cut the casing as close to the front of the car as you can, then remove the screws on it and the heater core is exposed, you may have to do a little more "customization" to get it out from there but not much, when you get the new one in, just use duct tape or some kind of glue in the seam after you screw it back on (after all duct tape is designed for heating ducts), it also fixes everything
hey while your at it, you wanna do mine too?
good luck
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88 Notch, B&M Ripper, 3.73's, Ported E7's, Explorer int. w/ ported lower, pulleys, 1.7RR's, BBK headers, off-road H-pipe, flowmasters, subframes, 65mm TB, March ram air ,MSD coil, U/L control arms, 155lph f/p, Crane Adj.FPR, Nitto drag radials, best 1/4--> 13.76@101.4 on a 2.17 60ft