Use a countersink in a drill motor, and add about a 0.05 champher on the gasket side of your NODULAR HOUSING. This will allow a space for the displaced material to pull into when tightened. If you file it away, it just becomes thinner and will prob do the same thing. You could cheat and install set screws with washers and nuts instead of the ARP studs, but you would have to epoxy them into place. The washer would provide greater surface to displace the torque applied when tightening. The mounting surface must be too thin to start with .
Give me a call if you need and we can hash out different thoughts.
That is a good suggestion and I will probably do that as well. The displaced material on the housing appears to be from the hole size being to small and looks like the studs were forcefully pulled through. Don't think it was caused by the flange being to thin and normal torqing.