[hound dog]

You have the wrong pistons. Best to trade them in and get the right ones for a '69 block. Otherwise you can probably have someone skim the .015 off the top and maybe get by OK if the top doesn't get too thin. You'll also have to double check valve reliefs. Compression will probably go lower because the volume of the cylinder is larger per .001" than the relief cut into them. I wouldn't try to compensate for wrong pistons by juggling head gaskets either. Do it right the first time and you won't be sorry!
h dog