FWIW, back in the mid-1970s, I had a pre-64 Model 70 Fwt. in .30-06 with the same problem. I simply glass bedded the rifle using Accra-Glass, bonding the crack with the same material during the process. After cleaning things up, the repair was still holding strong until the mid-1990s when I had a friend restock the rifle for me with a nice piece of California walnut.
