Done it on a G body daytona. Remove glovebox, unbolt dash lower on passenger side by kickpanel, remove ac controller in dash. Disconnect heater and A/C lines under the hood. Disconnect 2 vacuum lines routed out to vacuum engine harness, and to heater mixing valve . One should be black, the other should be grey. One is vacuum in to the controller in the dash, the other vacuum under the hood controls hot water going thru the heater core. Several stamped nuts hold the whole thing to the firewall, once you disconnect all this, push it inside and down on passenger floor, pull dash back slightly, and remove it. There may be a strap inside holding it up as well, plus disconnect all your fan and controller electrical from the heater box. Then dissssemble, and swap heater core out. Theres some preformed foam gaskets you will prob find out these are prob dry rotten. Dealer should have these new for a few bucks
