Indeed MAX7456 is sensitive to voltages differences between analog and digital part.
So, power minimosd from common 5V from FTDI is a good solution, with the two solder blobs.
BUT, whay do you say you have to use old V1 ? Why not V2 with the…"
"At step 5, when you connect the Lipo with the balance connector, the analog part of OSD will be powered by the OSD regulator. Because the two solder tabs are bridged, this will also power the digital OSD part, AND the APM, AND the power module, and…"