Hey shachr,
Hows it going! Nice bike. Welcome to the forum.
About that piston issue. I'm not a professional builder, but you need to take into consideration weight and balance. Are you replacing the piston with a bigger one that weights more - 10 over? If the front piston weights more then the back you will probably get a vibration and the balance will be off. There could also be a fuel issue that the front will run a little leaner because of the added volume.
If it were me I would do them both and not worry about having any problems, might cost a few more $$$ but will be worth it in the end. Just my thoughts best of luck and lets see some picks in your gallery.
Lenny