Yesterday I wondered how op25 would do on my RPi pi 3 B+ using a 64bit kernel and complete 64 bit OS. So I downloaded Arch linux's basic 64 bit image to get the basic files I needed to manually build it up with the Mate desktop environment. I then nuked their /boot partition with a U-Boot kernel junk and it's modules and cross compiled on my x64 my kernel using aarch64 toolchain. I maintain this kernel for my friends on satellite forum which is at kernel version 4.20.0-rc1.
https://gitlab.com/Dark-Sky/rpi-udl-linux
Arch's 64bit image uses the kernel from kernel.org and you lose certain drivers which you need. My kernel is Raspian's from their 4.20 branch (with modified modules for satellite viewing) which has support for the missing devices that do not work.
I am still in the early stages building my image but got to the point that I have op25 running and it seems to be working good.
I want to tweak things for a couple of days but if anyone wants to play I will upload the 64bit image to my googledrive for downloading. It should work on the pi3b also. Just let me know.....
First pic is the kernel version
2nd pic is file info on /usr/local/lib/libgnuradio-op25.so that was built
3rd pic is my pi3b+'s Desktop with op25 working and the web interface. (Notice the cpu usage under System Information)