911 comp valve springs

I wouldn't use stock used retainers on anything. Almost all of them I have ever examined with a magnifying glass revealed cracks on the under side of the lip where the locks engage the retainer. This 331 Hemi I have for example. I didn't even need a magnifying glass. The center holes in the retainers were opening up from the cracks and valves were getting ready to drop. New retainers are cheap. Get some.