Mazda MX5 pistons seem to be the go from what I can find out & at 79mm, it would be a good idea to offset the bores a whisker & 'O' ring the block if serious performance is what you have in mind.

A copper head gasket is not cheap, but there are those who would recomend it.

This is the real problem with big bore sizes. The gap is so small that it is not possible to individually 'O' rong the cylinders & this figure '8' pattern becomes necessary. This is also why a small offset when boring will help.

You gotta remember that the A series engine was originally designed around a 73mm bore size, not 79mm.