It's a custom model, an AR91xx SoC. I don't know why dd-wrt runs on a different bootloader. Out of my league (don't have enough knowlegde about bootloaders, mtd etc).
I think like: if I can make a full copy of the flash (with OpenWRT/LEdE) and can store this on the other router, I have an exact copy. After that I can solve some issues and update the router with Luci.