Well a few hours work and some painstaking soldering with a nice pointy tip has given me this result.
Im not sure its "pretty" but at this stage i am sure its 99% correct. Ive buzzed the cct out twice so far but my eyes are tired and i know im either making or close to making mistakes, so ill buzz again tomorrow before im prepared to put the 100% correct tag on it.
Oh man theres some irritating fine trace work done here.
I took the board back beyond the corrosion and reworked it all using single trace copper strand. Some of the traces go 2 ways from the chip sockets, so 2 strands were inserted and then soldered along the track. Some i couldnt get to, or the risk of shorting logic paths was too high so i went along the back.

hate this work... but it done ( i hope!!!!)