G'day Chris.

If your US/EU 2xx7 has HWID 1582 it will have PCB P/N of 105-02283-00 or 105-02139-02 which matches those of SG/MY 2567's HWID 1722. Theoretically cross-flashing is possible because even though the HWIDs don't match the PCBs do. Safest way would be to use US/EU boot.bin combined with SG/MY fw1_resources.bin and fw_all.bin to create a hybrid RGN file retaining HWID 1582. If after flashit you're faced with 'system software missing' message, you could try a full flash to HWID 1722 using the full SG/MY firmware, but that's much riskier and could brick it. Using original boot.bin and HWID should be reasonably safe and reversible, but any flashing of this nature carries some risk regardless.

If your unit has HWID 2077 best don't attempt to flash SG at all as i think it'll brick for sure.

Current SG/MY fw is V3.50 which is only available via the Asian 'Garmin Updater' by running it's launcher.exe with a qualifying device attached. V3.40 is still available on the website here:
Code:
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Don't run the nuvi25x7_SG_v340.exe file, extract it to find the firmware GUPDATE.GCD in nuvi25x7/.System to make your RGN file.