A520 modulator schematic?

[freqmax]

Where can one download the schematic of the A520 modulator?

I know there's better chips than MC1377P but the original schematic has some info on how the problem was solved then. And it's a starting point.

As an alternative to reverse engineer:
http://amiga.resource.cx/exp/a520

And hope that the PCB is no more than dual layer..