I have a Question
 

I have a 1981 porsche 911 targa I'm going to rebuild my engine a 3.0L I wanted to know realistically what is the most housepower can i get out of my engine naturely asperated and if I where lets say to change my engine to a 3.2L will the car be worth less. Basically is it better to have the original engine or a engine from a newer model.

Buy "How to rebuild & modify porsche 911 engines" by Wayne R Dempsey & read it cover to cover, also get on instant-g.com & hit the 3.6 conversion button

The sky is the limit.
Search is your friend here; it's been covered many times.
Try my handle for building a SS 3.2.
And no, a different engine with more horses will not decrease value.