Different manufacture barrel bands fit different manufacture stocks differently. That's what you're dealing with. Not all of the original 03A3 stocks were made to the same dimensions.
Most will swap out without damage, but you may have to look at a different stock and/or hardware until you find a set that fits without damaging one or the other.
I also had an issue where the stock hole for the bolt was drilled off center relative to the band. No matter what, it wouldn't line up. I had to drill out the stock quite a bit and for a permanent fix I'll need to fit and glue a dowel and then re-drill. May be worthwhile to verify the hole with a small punch before you go further.
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