Grant,
Your biggest problem IMO (besides not being able to buy pistons) is sorting through all the BS in this thread. 0.080" overbore is the practical limit for an endurance engine, but some racers push to .125 and fill the bottom end of the water jacket with stabilizing epoxy and rely on water in head and upper cylinder jacket to do all the engine cooling. In the reading I have done between Leo, Bill Fisher and Roger Huntington, lots of folks push to 0.080 and beyond without problems as long as core shift isn't a problem.
Heat dissapation has not been mentioned once in the discussions of any of these authors, however, each of them have mentioned the reduction in wall stiffness. Make sure they use a boring (torque) plate to pre-stress the cylinder walls, your chances of having nice round bores under assembled conditions is much improved.
