That really changes things, stainless on stainless can almost weld themselves together when the chromium oxide layer deteriorates, the Heli Coils are usually stainless. Nickel anti seize is a must when using stainless bolts in them.
Trav is the man, 1/4 is close also but i not metricTap it for M7x1, it takes an M6 hole, just run an m6 drill bit down the hole then tap. The M7 bolts are commonly available at Ace or HD.
Tapping for M7 takes a lot less meat away then tapping for a coil or sert. Make sure the hole in the part being bolted on has enough play for the extra 1mm (it usually is no problem), the head will be 11mm instead of 10mm.