Right... FPU Sorted!
It was the FPU socket that was causing the problem!
Now... Confession time:
This one was probably my fault for using the FPU socket as a handy place to poke wires into so I could hook it up to my scope while I was debugging the failed CPLD.. Wires that were probably too big and ended up expanding the pin holders in the socket such that a number of them weren't making good contact with the smaller diameter FPU pins when the FPU was in place.
Anyway, I managed to source a replacement FPU socket, de-solder the old one and replace with the new one. Once in place, not only does the FPU work, it seems to work reliably at a synchronous 55.55MHz... Result!
Also nice to see Dhrystone is on-par with the '(AC)A1233n-55' benchmark in the module downloaded here: http://wiki.icomp.de/wiki/ACA1233
One final thing I need to check is the clock port... I'm 99% certain there's a couple of opens from the expansion slot connector to the clock port headers that'll need a couple of patch wires, I'll see if I can source an RTC board to plug in and test.
Feeling pretty chuffed to have brought this board back to life thanks to Jens' help, and can now sit happy knowing I have one of the fastest 68030 based accelerators ticking away in my A1200
Cheers,
Graysters