Welcome to the Darkside. I just purchased a 65 Cat Convertible last year. I love the car, I rebuilt the steering and suspension, and it handles like a dream. A 60's full-size pontiac is one of the best looking cars on the road, and will get more looks and attention then you can believe.
For more info, I would also recommend the following websites:
www.fullsizepontiacs.com
http://autos.groups.yahoo.com/group/pontiacdarkside
http://autos.groups.yahoo.com/group/pontiacbigguns
I too would recommend the Long Branch Manifolds, you can check them out at
www.ramairrestoration.com
Just one more thing, Don't believe that it will be easier to drop a chevy motor in and make more power. The Pontiac motor is a monster with the right parts, and a full size pontiac will want alot of torque.