Okey, so here's some new mods going on. Nothing is permanent yet, but the preparations are done!
Removing the pop rivets
The holes left by the pop rivets proved a little to big for the split rivets I'm going with eventually, so I'm filling the holes with ABS-paste, here I've only covered the front of the hole with standard masking tape.
Filling the holes with new plastic
Since drilling out the pop rivets proved a little more challenging that I had expected I'm going the lazy route on the knee belt and just filling it with ABS-paste. Might replace that with putty and paint it if this fails.
I'm going with standard paper brads for test fitting everything before making anything "permanent" with split rivets.
Here's the crotch strap I remade in elastic rather than the webbing I had before.
Here's the outside view
Here's the connection between the kidney and ab plate. I'm using standard washers on top of the elastic for strength and nothing underneath the elastic.
The outside view
Test fitting it on myself
I'm feeling quite comfortable using this setup and going for a more permanent solution with split rivets. So if you think I'm doing something terribly wrong, please tell me now.