For the wheels, what fits a Chevelle does not always work with a 68-69 Pontiac in the front. Chevelles have larger front wheel openings and different internal structures in the rear.
What width wheels do you want to run?
Do you only want a 2 inch drop or do you want to set the fender a specific height above the tire?
More than an inch or two takes a little more than just springs to make the front suspension work. If you want to change spindles I would recommend the AFX tall front spindles and use a brake package to match. This would lower the car about an inch in the front and really improve the handling to match the new brakes and tires.
Here is my 68 with 18x9 front and 18x11 rears:
Let me know if you have any questions about my setup.
Jon