For some reason I can't find the sources I had that prove my point ans I won't be driving to California any time soon but I can support what I said with a few things
First, an engine with only two full sets of rods timed at 120 degrees would be prone to binding especially when travelling over uneven track. The Romney Hythe and Dymchurch railway in England at one point haduring some 3 cylinder locomotives and one of them was experimental and the pins were set at 120 degrees like a shay, it was notorious for having trouble with binding. If you could add a full set of side rods, that would alleviate the problem of binding.
Beau Brandstetter