Andre, Per Collias' MoPac Power, the Pacific RR--the main branch, as it were--regauged July 18, 1869. It does NOT clarify whether or not the SW Branch was included. FWIW, the reasoning had to do with the opening of the Eads bridge. Prior to that year, there was a MO law--based on James Kirkwood's recommendation--that established 5' 6" as the gauge of MO RRs. He promised that the Mighty Mississippi would never be bridged and so wanted a wider gauge for more volume capacity. (As a mostly irrelevant aside, the St. Louis & Iron Mountain built to 5" 6", and they had to change twice, once to 5' (1969) and then to standard gauge (1879). This data is also at variance with that posted above. I have my MoPac handy but not my Frisco or my Miner book, so I can't compare the references.