Ok- write up for doing the heater core on my '70 sportsroof.
Get someone else to do it (if not, go to next step)
If too stubourn- unhook lines going to firewall (if A/C- unhook those too).
On my car I pretty much had to pull the entire lower dash off, along with the upper dash, glovebox door, console, etc to get the damn thing out.
Take lots of pictures, invest in the manual, and grab a 12-pack for the celebration cause once you've finished you do have reason to celebrate.
Also- good idea to get heater core and/or evaporator pressure tested while they are out.
THe Swede