That's the BIOS binary - what I was after was the flashing utility alone. I managed to get a good newer version of Winphlash to do the job - version 1.6.7.7. Offon - many many thanks for this - I have now flashed with this BIOS and can be 2nd to confirm for the NC10 community that this works perfectly with OEM SLP keys and ASUS cert files.
The SLIC table I extracted from another Gateway model said GATEWASYSTEM originally. It didn't work either, so I changed it to GATEWAM300 to match the RSDT table in my attempts to fix it. Is there something special I have to do with the RSDT table? I hesitate to mess with that one because of the risk of bricking the laptop.