Do you have to buy these when you install new rocker arms and springs?

 

You don't have to have them but they are nice. Generally help the rockers to not come loose.

 

AFAIK you need poly locks with Comp Pro Magnum RR's. Just make sure that when you order the locks through Summit or wherever that you get the right shank size (outer diameter) otherwise you'll have to grind them down to fit.

 

Poly locks are for roller rockers. I'm not even sure they could be used with stock stamped rockers, although if you retain the oil ball I guess they could, dont quote me on that though