Yes, that would fit in a 1040STf(m) chassis. It has no modulator, and you can add another 512 kB by just populate the empty places with 16x 41256 DRAM. Maybe you need to add another resistor on RAS/CAS lines between the DRAM and MMU chip (the square one directly right to the DRAM), the photo is too small to see if it is popoulated or not. If you need to add the resistor, check the cirvuit diagram of 1040ST on https://www.dev-docs.org/docs/