Terry and Gubi,
The tool for pulling the Alfa radios of that era is similar, but not the same as the universal DIN tool sold by Crutchfield, etc. The Alfa tool (on top in the photo) seems to hold the head unit much tighter than the universal tool.
Remember, these radios are "pull-out" decks, meaning the whole deck was designed to be pulled out of the car and taken with you to prevent theft. If they haven't been removed in a while, they can be stuck pretty good. The Alfa pullers also functioned as a carrying handle.
Once you pull the deck out, there is still a standard DIN sized frame you'll need to remove by bending the tabs down, and then you can unplug the wiring from the back of this frame and install your new deck.