I messed around with genlocks back in 1998 (I haven't used mine since then but I intend to get it going again) and I found that the easiest way to do what you want to do is by using Scala MM400 (or in your case Scala 300?).
But I must tell you that before I got my A4000T I found fullscreen animations to play back jerky on my A1200 (030 50mhz). When I got the A4000T with 060, I would have the biggest animation already sitting in RAM (128mb) and then I found it to play reasonably smooth through Scala MM400. If it wasn't for the sound commentary I would probably have just dumped it to tape with mainactor or Clarissa (can't remember if that was genlock compatible, but it was smooth!)
Some stuff you could use:
http://unicorn.us.com/jacosub/By the way I believe that Supergen 2000s only works on A2000 computers.
A while ago a dude was selling a Lola 2000 genlock on Ebay. It started at £5 with no reserve. I don't know if he sold it or not, but if that comes up again, snatch it up! I have one of those genlocks and it is awesome.