They are not the same, but from what I get the rubber seal on the piston is the same - comparing they looked identical to me (although without removing the one from the rear). Good news is, the full rebuild kit is now sold from Zed Parts. Not sure about the dust boot though, I was lucky to get one from eBay.
If your piston seal looks good, and the bore looks alright, I would suggest honing it by hand with compounds and 2000 grid paper for wet sanding. I did that and the brake is rock solid - although still on the center stand, but I have no reason to be not confident.
Mine front - sent it to be re-sleeved with stainless steel as the bore was shot, put a brand new kit put in, and this should last virtually forever. Front brake is way more important than rear, so I would suggest concentrating on this.