The board appears to be from a 1040 and appears to have been upgraded to 1.5MB. The bottom row has 16 x TMS4256 chips. The top row appears to have been upgraded with 16 x MB81256 chips.
Some other mods appear to have been done:
- Extra cap top left of memory row.
- Extra chip and A/B switch added to board near drive. Chip is glued down so can't see what it is.
- Wire from Video section to modulator. Might be stock.