mcu to vga
It was long time ago. I dont have any schematics at this time. I dont even know if NEC upd6450 or 6453 are still in production. So you better decide on which chip you want to use first. There is an 8051 derivative (perhaps from Philips) that has OSD built in.
The interfacing of upd6450 is quite simple actually. If I remember correctly, it had 4 serial pins to connect to microcontroller, a few for oscillator and more selection, a video in and a video out.
If you really decide on the 6450, I will try to fish my old records if I can find some notes.