The rear brake caliper dust boot cannot replace?

Yes, the simple way for this problem is totally change two rear brake calipers. But I tried to rebuild it first, the caliper got stuck and moved difficult, I tried to fully open it and clean inside the caliper, the dust boot broke when open the caliper.
I have bought 3 caliper repair kit, but all the size can't match.
Pic1: the dust boot in the picture
Pic2: the general caliper piston part picture, the open hole is a simple circle
Pic3 my caliper, the piston open hole is special two edge
pic4 the caliper repair kit

The original dust boot is a soft base ring, locked in the open hole second edge, I don't have the photo, but the repair it is a hard base rubber ring, someone said there is a steel ring inside the rubber

The piston first inner diameter is 51mm.
The piston second outer diameter is 55mm.
The rubber dust inside diameter is 50mm.
The rubber dust outside diameter is 55mm, see the pic 5.

It looks like I can't install this, any idea?
The rubber only press the outside diameter to 51mm or extend the inside diameter to 55mm, otherwise I can't install it back, but there is steel ring inside the rubber, I can't change the size like this.