So my thinking was that with the bolt face rim gone and the extractor now unable turn on the rim. You could create a small channel farther back on the bolt body and move the extractor lip back so it would be able to still rotate as if it was original but farther back on a channel rather than a rim. And since only half of the extra size of the rim would effect the extractor. Has it still have to lay even with the firing pin. You could mill the small cut out for the extractor that difference and heat and slightly bend the extractor tip up so it still fits in the cut out. Grips over the 45-70 rim, and extractor guide can ride on a channel on the body