[SSedan64]

You don't have to use the spacer. It's just extra insurance. Some worry about the cam rubbing a hole in the rear cam expansion plug from using it to align the timing gears. With the spacer the cam never touches the rear plug and it keeps the timing gears aligned. Rollers don't really have any rear thrust like flat tappets, they just float a little. The rear of the cam gear rides against the spacer like in a Factory roller block. If the engines a race only that's pulled frequently you can keep a close eye on the rear plug if not usuing the spacer. Also you can use a factory rollercam retainer with the mounting tangs trimed off.