Anyone have a tweaked aircraft file that works (747-8)? or load manager?

Has anyone successfully tweaked the aircraft.cfg file for the 747-8? Like most of my payware, I have tweaked the basic things like weights, thrust etc, to bring it inline with the real thing, and in most cases this works, bar perhaps the odd FMC that doesn't like the changes re fuel predictions, but with the 8 I'm finding she will dolphin up & down in pitch even at FL270, M0.85, and 50% fuel & payload, something which normally occurs when you climb to too high a flight level while too heavy. The other thing to note is the load manager will obviously only recognise the 400's figures. Anyone found a way to tweak that at all?

Cheers

Simon