The ODM for both devices looks to be Senao. There's bunch of clones already supported by OpenWrt.
Anyway, before flashing random firmware make sure partition layout is same, otherwise sysupgrading from initramfs could overwrite crucial data, like bootloader or wireless calibration data. To get the partition layout check kernel log or run cat /proc/mtd
on the Riverbed running original firmware. Also check bootloader booting command if it's loading from proper flash memory offsets.
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