Go with the MCP, Brackets may or may not have to be made but otherwise it’s pretty straight forward and will be an upgrade in braking power to a lot of Euro brake systems. I’ve done several conversions.
I also share Greg’s sentiment on MCP. We have an new chassis build we are working on here that utilizes metric components like a 50mm rear axle, rear hubs and front hubs/spindles and wheel bolt pattern. After some research, the MCP system was what we went with. Been great to work with them and has proven to be a great setup with minimal effort on our end to adapt their existing system and mounting hardware.
Definetly MCP they aren’t hard to adapt they aren’t expensive and they work great. If you combine the standard caliper with the small bore master cylinder You’ll have a little more pedal travel but very effective breaking.
You might want to call Coyote Kart in NY. They make a 50mm kart that uses MCP brakes. They might have a bracket that would bolt right on to your bearing cassette.