I have recently almost completed a V2 to these drawings and unless I have been exceptionally lucky or perhaps stupid enough not to have noticed errors, have had no problems bar one. That was in relation to a part of the valve gear, the radius rod, where I found the cut out portion that connects with the expansion link to be about 0.030" short (at the engaging end). I believe that others have also found this to be the case.
Another part that caused me grief, but that may be down to lack of expertise on my part, was the return crank. These have very little metal on them to enable them to tighten up on the crank pin with a 10BA screw and successfully hold position whilst under steam. I eventually resorted to threading the crankpin, thickening and tapping the securing end of the return crank and just for luck, a blob of loctite. Overkill maybe, but it was the only way that I could get the blighters to stay put.
Mick