You might check out
http://www.autodelta.de/
Lots of great historical photos and information on
these rally cars.
They are actually selling some reproduction body
pieces made from the group4 car—tempting to
build a rally replica—but it would be really hard
and expensive to find all the right pieces to make
anything close to the "works" cars.
Autodelta also ran Alfetta group2 cars which seem
to be about as rare as the Turbodelta Group4 car.
The car Portal Classic has for sale is the homologation
steet car and very similar to a standard Alfetta GT, with
the exception of the turbo and a few other little things.