I 've replied asking for any further suggestions but I'm yet to hear back..
Spring lengths OSF accuracy as best possible with a tape measure on reasonably level ground. Unable to reach to measure spring with wheel attached so simulated by raising/lowering hub:
Minimal pre-load, full droop: 200mm
Minimal pre-load, horizontal wishbones: 175mm
Minimal pre-load, fully loaded: 150mm
1 thread visible above top perch, full droop: 185mm
1 thread visible above top perch, horizontal wishbones: 155mm
1 thread visible above top perch, fully loaded: 142mm