Most real custom gunmakers won't touch them for a custom job. The tang safety is probably the best model, but al M77's have proprietary design features, including their unique bedding systems (like the angled front screw) and non-standard barrel tenons which present challenges. Those, in turn, require specialized jigs and tools for proper truing, making barreling a challenge and costly. Second unlike the 98 or Remington 700, there is a very limited supply of aftermarket parts like triggers, bottom metal, scope mounts, and other components, which complicates and increases the cost of customization. Third, There may be some, but I don't know a single custom maker who would have much confidence in an investment cast action for such a project. Fourth, the relatively short magazine box limits cartridge options. Finally, you need to think through eventual resale. Not many will be particularly interested in a custom rifle based on the M77. Unless your name is Jack O'Connor, no custom rifle returns its investment, but a Ruger based one will be worse than most.