Hi
Mutt,
Not quite sure what you mean when you say
(Old Smokey, this one came from your part of the world), I presume that you mean that it was bought from us. I never had any part in the fidelity checks of the B747 classic, but be assured that if you'd bought any of our B777 simulators that they will always accomplish the RTO 'better than the book'.
I suspect that your first point is the culprit
"The UK rebuilt FFS isn’t 100% accurate". Did the rebuilder use the data pertinent to your aircraft version (Brakes / Spoilers etc.)?
And then there's the tweaker's dilemma, I've spent thousands of hours doing fidelity checks on other simulators, tweaking up one aspect of performance to fit the Manufacturer's performance data exactly, and losing it somewhere else in the process
Good luck with the new toy,
Regards,
Old Smokey