If anybody is interested:
I've recently got a hold of the vendor sources for the Check Point L-71 (1430/1450) firewall appliance.
Since I haven't been able to find them anywhere on the Internet, I've decided to archive them on GitHub:
So far I haven't got much time to look into them, but I managed to boot mainline Linux on my L-71 appliance in the past. Just without a working device tree.
The archive includes their modified Linux kernel, bootloader code, as well as a toolchain for building.