It can be done. It seems like the two are different animals and my best guess is that you'll have to yank the whole unit and install one that has the appropriate guts.
Inky05 has a
tech tip for converting to an internal coil HEI model.
There's also a thread in this very forum in which clarifications are made.
Hopefully this is helpful and that someone who knows better than I comes along and sets me straight if I'm wrong.
