This is a straight-forward suggestion. A new timetable taking the Diesel Legends of the Great Western timetable but substituting the Blackpool Branches 47s for the services operated by Classes 52/47/45. Many of the 47's from Blackpool were allocated to the Western Region of British Rail at the time and those from other regions would be seen from time to time. As an extra, the Class 47/4's repainted in an approximation of Great Western Railway lined green could also be added. These would be 47484 Isambard Kingdom Brunel, 47500 Great Western and 47628 Sir Daniel Gooch. 47079 GJ Churchward would not be appropriate, being of sub-class 47/0. This could also be an opportunity to add the Class 50 as dlc. In 1986 most examples would have been in large logo livery. However there was also 50007 Sir Edward Elgar in GWR green, and the first examples painted in Network South East red/white/blue/grey. If memory serves these were 50017 Royal Oak and 50023 Howe. Right that's enough day dreaming. I'm off to see how many Blackpool 47's I can squeeze into GWE in scenario planner.
The Blackpool Branches Class 47 is not appropriate for DLOGW as it is a later version with high intensity headlamp which were not a thing in the early 1970s. Likewise, the Class 50 was still a WCML machine during the period, appearing on the GWML a couple of years later. Appropriate classes for DLOGW are... 22 diesel hydraulic 35 diesel hydraulic 42/43 diesel hydraulic 117/121 dmu 123 dmu 128 dpu 251/261 Pullman sets
In fairness, period accuracy is not the issue here. None of those are accurate for GWE as depicted as the route is created as it was in 2016, long after the trains featured were turned into razor blades. So if we can accept trains from 1973 on a route from 2016, and can also accept trains from 1986 on the same route, then I would love to see the above.