I just cut the pipes after draining the water and the old core slid staight out no problems and put the new back with 2 bits of hose and a couple of hose clamps....(some aftermarket company actually make a replacement heater core that has a flange that screws together to do the same thing)...that was a fair few years ago....you dont have to drop the air con or too much of the trim and it isnt a huge job to do it this way.
This is my vr that I rebuilt ....CLICK HERE to see my vr on Cardomain ......if you want to check it out......Anyway make sure you rubbish a ford daily ....I am a 4DH8RZ Club lifetime member .................new members joining everyday
cutting the pipes is a quick and easy way of fixing the problem, but if you want a proper job its not to hard. just give your self plenty of time to do it. the dash comes out pritty easy. once all the console and trims are out its only 4 screws holding it in. the hardest part is putting it back in and running the wiring loom witch is cable tied along the back of the dash board. your A/C has do be degassed as it connects to the heater box near you wiper motor. the heater box itself is only held in with two screws on the trans tunnel a couple of screws holding the fan section to the firewall and three screws threw the firewall that you have to undo from the engine bay. i would say the hardest part of the hole process was the steering colum witch has to come out. theres only 3 bolts on the mounting brackets for the colum but the bolt and nut that hold the colum to the imediate steering shaft is really hard to get to and you can only turn it a 1/4 turn at a time. after doing mine and re-installing the colum my steering was really stiff, two days later i instally ectractors witch meant the stearing rack had to come out, upon re-installing the steering rack my steering was all of a sudden back to normall, figure that out? all you need is a gregory's manual and some time and anyone can do a heater core i think, just dont forget to degass you A/C or you'll get stuck half way threw the job. i took photos one all my dash was out and then back together but was to into it to stop and take progress photos sorry.