In terms of pin loading and amplification of errors in rocker driven valves, there are two things to consider. One is the degree of amplification - the Bulleid gear is doing quite a lot at 3:8 (2.66x increase). Even in the fairly common examples of Stephensons gear originally arranged to drive slide valves below, instead going through rockers to drive long lap piston valves above, I think it would be pretty rare to see a ratio of new valve travel to old as high as 2. The GWR inside-to-outside rocker drive on the outside cylinder engines drives the valves in the same direction, so the pivot only needs to provide the additional load due to the increase in travel, not a full reversal of the increased load. That said, I was mostly commenting that the 3:8 levers in the Bulleid gear have a lot of opportunity to mess things up with the valve events, and perhaps not the most maintenance friendly.