I believe that British Airtours did a Gatwick - LAX rotation stopping at Winnipeg outbound (I'm not sure about inbound) and that would probably have been a 136.
I know from a flight deck visit that 136 & 236s were operated by the same crews. I believe that they also had the same pax configuration. I was travelling to Toronto on a 236 which was probably a late substitution. The same could be done in reverse but at the expense of payload for a long distance route. Pan Am operated to the West Coast for many years with 121s although they really weren't really suitable and were very payload restricted. Of course anything operated by a 747 before the 236s arrived in, I believe, 1974 but am happy to be corrected, would have been a 136 operation.