A Mason Boggie had to be much worse staying in time than a southern valve gear engine which itself went out of time due to the main driver lifting. When you consider the rough trackage a Boggie ran on I bet they were slippery caused by the timing variation of that crazy valve gear. In addition you could go dead center with the driver lifting. and have to reverse the gear to move some so you could go the direction you wanted to go making switching a little more of a headache.
I have seen one of those in 2.5" scale and that exhaust timeing can wonder all over the place.
Just my thoughts.