you should be fine with an 80 amp alternator
here is how i figure it
the stock alt was about 63 amps at the most (right guys?)
and the only draw you are adding is the fan at 13.5 amps
your cd player takes very little power and should use close to the same amperage as the stock radio
so by that you should be fine
another way to look at is that I have a very similar setup with a fan that draws something like 25-30 amps but i have a 100 amp alt and everything is fine, with the fan, headlights, cd player and heater going i still have close to 13 volts

but i dont know what kind of fan you are looking to put it that only draws 13 amps, what is the cfm of the fan?