Did this board run before the modification with the other components or just a first try ?
Maybe you just need another setting of trimmer R2 on the ZX8-CCB module as there is no Ferranti ULA inside but a rework (with possibly other voltage levels at the output). Just make a photo of the trimmers position and try to slowly turn R2 to see, if the cursor will appear.
By the way, the second black cable from the ZX8-CCB module is not necessary to connect to the modulator, one GND connection is good and enough. The brown cable can be feeded through the free third entry of the modulator. That makes you able to close its case.
When looking at your board and the description of vLA81
https://vdrivezx.com/vla81/
it is a simple replace plugin for the ULA. I think the black wire from pin 35 of ula (clk input) to pin 3 of cpu (A13) is wrong. I would remove this. And by the way, the vLA81 has a powerful video composite output and there is no need for the ZX8-CCB module at all. You can directly use a wire with a capacitor 100uF inbetween as described for the vLA81.
