The sloppy fit will make it easier to line things up. Unbolt it and place the little seal that you forgot between the halves. Maybe after this we can get that little car down off the jack stands…maybe. Remove all vestiges of the rubber seals and crud from the pistons and caliper bore. Disconnect the flexible line at the flare nut end. Robert, You can also check with Peter C at http: Midget Brakes 1
You can cut the hoses off, then use a socket over the crimped end and a wrench on the nut to disassemble frozen connections from their brackets.
Apply increasingly higher pressure to the line, until the pistons move. From the looks of the rotors you have some pressure in the system so you might not be as bad off as you think. Pull the caliper off the car and watch for some bow-tie looking shims that may be between the caliper and the axle. Related MG Midget Pages. Use compressed air to pop the pistons out.