These two are pretty similar to each other:
CPU: Z80 @ 3.579 Mhz
VDP: TMS9918, 16k VRAM
PSG: SN76489
RAM: 1k (SG-1000), 2k (SC-3000)
ROM: 0k
For maximum compatibility I've limited the RAM availability to 1k to work on both machines.
This port should now be firmware independent and as a result -subtype=rom now works, and hence the SG-1000 is now supported.