Lots of answers on the forum for this, pays the money etc. Hacksaw a groove down the radial line of the pads , coat the back of the pucks with copper grease, use EBC pads, grit sand the existing pads. All work to some degree. Keep the puck and the pivots well lubricated with silicone grease and she will stop but never as good as a modern six pot caliper bike. Consider a dual disc conversion which will improve matters somewhat.
Me I've doe all the above and she she still squeals but the thing stops. Fellas in tin boxes hear me comiing so I guess thats a plus.
Ride safe
Blind Bob