I am changing out a leaking heater core in my 1988 s10 blazer. I am following the directions given in the GM service manual which lacks a lot of detail. I have disconnected the hoses and mounting bracket on the engine side of the firewall. Inside I have removed the screws from the rear cover of the heater assy case but cannot completely remove the rear cover because of a lack of clearance with the rear of the dash. Does the dash need to be removed or loosened and moved to remove the rear cover and heater core? Any help appreciated.