At the u-boot prompt you can run the command 'printenv eth1addr' and copy the output. Do the same for each of the remaining network ports mentioned in the Restore macs section of the OpenWrt wiki page for this device.
kwboot is an application, I'm not aware of a windows version so you'll need a linux device to run kwboot application. UART Booting HowTo for Selected Kirkwood Devices is a good write up of using kwboot.
Never hurts to save all the params in the uboot env, just C&P them after running printenv.
https://forum.doozan.com/ is a gold mine for Kirkwood owners, not really focusing on openwrt, but there's a ton of useful info about the devices there.
My guess is you first have to (re)boot and interrupt the device during very early stage to actually see the original u-boot, maybe press certain key to halt the boot process.
If you made it to the original u-boot, you may save the stock environment variables first probably all with printenv. From that point the wiki is insufficient how to backup original bootloader/roms but you may try help to see what options it give and report back?
Certain checkpoint devices have 2 serial ports, the one on the outside of the device can be a virtual console which will only initiate after booting the kernel. Maybe check inside the device if there is a internal serial rs232 pinout which may cover console output during early u-boot & kernel console.