I did that exact job; first find the balance point of your GM barreled action, then mark the balance point inside the groove in your stock. Next, wrap your original carbine barrel in blue painters masking tape. Then wrap 80 grit sandpaper around the barrel and use it as a sanding block, starting from the balance point and working forward. Open it some, check fit, repeat. Then go to 120 grit, and finish with 200 or finer. Take out just enough for a press fit, or you can do the job with the rest of the barrel floating beyond the balance point. Stain the groove; Birchwood Casey walnut stain is a good match, then seal with 3-4 coats of Tru Oil.
