Two S&S holders arrived yesterday, and they're about 1/16" too long. The film plane depth and everything else seems right, but they just don't seat properly, and I checked the back thoroughly to make sure there was no obstruction. The previous owner of the camera used it with standard holders, so they should work. I wonder if quality control is slipping with increased demand for these, since Lisco/Fidelity stopped manufacturing 11x14" holders.
They'll be easy enough to fix, and I'll ship them back on Monday, but at $300 a holder, one could do without the hassle.