I have heard of sirion brake upgrades for the L25Xs. Unfortunately, I don’t know what’s involved, but, If you can fit GVTi brakes, then you can fit Copen brakes. Copen would be the best bet as they are the biggest and are used as an upgrade for the Sirions.
If Sirion rear drums fit then a G100 drum can be machined down to become a carrier and hub for an Applause rear disc. Applause disc bracket will prob fit, but may need it’s centre bored out and some spacers made to offset the caliper. It’s pretty much a flat plate and would not be to hard or a job for a fitter or turner. Applause or MX5 rear calipers (some share the Daihatsu part number) will round it out.