Hey mate I just asked a similar question and I got two good responses. Looks like it wont be that difficult to do.
I am actually doing this tomorrow. It will be in Wantirna, Vic. You are more than welcome to come and watch (and help

) if you would like to.
Send me a PM with your number if your local and wanna come see. Other wise I will try to take photos and make a doco but no promises on the pics as I might be pushed for time.
Here are the quotes:
Quote1:
nothing real special.. just be careful near the vac operated doors as the arms do break easy.
the box is screwed together.. a couple of flat tip screwdrivers and a stanley knife to hack through the old silicone works best.
and a little trick.. do it out in the sun as when its warm.. the stuff is easier to seperate. i hated heatercores in winter when i used to do them for a job..
i cant remember how many phillips head screws there are, but i'd hazard a guess about 20??. and there is 2 that are in a deep section that you may miss.
so when lifting just do it carefully so you dont break anything
the glue is only in the bottom edge of the box so it isnt all the way around.
i used non hard setting silicon last time as its a kent to get back apart if a hard setting one is used.
with the new core.. you'll notice the pipes dont fit through the 2 holes that ford put in for the pipes..
just cut out the required plastic as trying to remould the pipes can easily crack the heatercore
wont need to trim much off. just test fit the top a few times to figure out the required amount
it will easily clear the holes in the firewall. its just something that was changed when the aftermarket cores were made.
oh and lastly.. if you have the coin.. do your blend door motor (im presuming you have climate control)
they are insanely easier to do with the heaterbox out than still bolted to the car.
Quote2:
i just put mine back together in my el just afew hours ago.the box is the easiest part i didnt even silicon mine back together didnt really see a point in doing it.just pull off the dash then the screws from the inside of the engine bay (firewall) disconnect heater hoses and aircon hoses and thats pretty much the hard part.took me afew days bcos i didnt have a clue what i was doing when taking the dash out of the car so that took me a while but the heater box is simple.take off all the screws, split the box in half take out the heater core and just change it with the other one.theats the simplest part hahaha good luck with it.