This is what I was afraid of. Here's a pic of my compliant fixed stock. Notice the pin in the stock itself. It doesn't go all the way through, so I can't just knock it out. Even if I could, there are no holes drilled in the bottom of the extension tube so I couldn't lock it in any position other than open. Fortunately, the castle nut is hardly staked, so removing the whole assembly should be easy. At least I can re-use the spring and buffer...
