A de-smogged engine doesn't like to be advanced as quickly as a stock one. You may get a little pinging on hard acceleration without the re-curve. Running a higher grade of gas or retartding your base timing a little will help until you can get the dizzy recurved.
HAC is High Altitude Compensation. A recurve is not a requirement, but it sure does help. The second spring on the Cruiser's distributor is so stiff it simply won't allow it to advance beyond a certain point.