Struck gold at GCR today - Register of West Coast Joint Stock by Casserley and Millard (HMRS). First mail train on West Coast (LNWR) in 1859 but their TPO's only ran to Carlisle. In 1879 LNWR and Calidonian agreed to provide sufficient vehicles for through running. Oldest vehicle included built 1860. Although in 1885 the post office complained about coaches on other services being a bit old - one of which had been built in 1848.In 1864 George Landsdowne patented his improved gangway (PO type side one) and PO had to pay 14 shillings per gangway till patent expired in 1878. So now we move the offset gangway back to before 1864.
Few lines later they mention that the first LNWR gangway connections for pairs of vehicles (dining cars, saloons etc) were offset initially but they were found to be inconvenient and soon after central connections were built instead.
So Greg, will that do ?
Cheers, Simon