You're making a simple repair way too complicated. You're not seeing the forest because of the trees. Those two smaller bolts, one of which you stripped, aren't there mainly to hold the caliper halves together, that's the job of the two bigger bolts. These little ones are there to insure a good seal around the fluid crossover. Their low torque spec is a clue for this. They simply maintain even pressure around the crossover hole, not letting the caliper spread open there under brake fluid pressure.
I already mentioned the Helicoil repair and think it would be perfectly acceptable here. You want stainless? The Helicoil insert is stainless, and properly done in alloy, the repair is usually stronger than the original threads. Not that it needs to be, this is a low torque fastener. The biggest bad thing I see about going to a larger bolt is that this is a countersunk Allen. Not only would you need to drill and tap the threaded hole bigger, but you would most likely need to enlarge the countersunk area as well. The new larger bolt will most likely have a larger head. This is all way more work than a simple Helicoil repair.
