I've had a blown small block for 27years. Your picture of both the head gasket and the piston look familiar. I did find the cure. I haven't failed a piston or head gasket since 1991. In fact, a few years ago I replaced the block with an R Block and used the old pistons. Detonation caused by too much timing. Start with much less. My bet is performance won't be affected at all. Mine wasn't. I went down the trail of low compression and going WAY rich on the carbs,it didn't help at all. I learned by the time I bought my 3rd set of pistons.
Good luck Doug