I did end up getting a logic analyzer and from what I can see between the A570 and the edge connector is that with the 030 the BR/BG oscillates a few times whereas with the plain 68000 it's steady and reliable. I haven't really worked out why.
I'm not fully understanding it yet (and have had it all packed away for a little while). This all happens well before autoconfig so I'm sure that's not the issue.
I'll get back around to it one day, hopefully a little bit wiser and make a little more progress

- 2020-05-24 15_21_54-LA2016 Connected - KingstVIS.png (144.04 KiB) Viewed 3122 times

- 2020-05-24 10_34_37-LA2016 Connected - KingstVIS.png (131.1 KiB) Viewed 3122 times
Sorry I don't have a zoomed in one showing the issue more clearly. I was testing with a TF530 as the firmware was available to play with (and it was clocked slower).