Thank you for all these; I have not had time to include the last few things yet, but they are all appreciated: I will add them when I get the time.
As to the hypothetical Kestrel, that is an interesting innovation (and it is noteworthy that we have very little in the 1970s). The livery seems off, though: the wrapped around yellow ends only came in with the large logo livery at the very end of the 1970s; the original livery should be the same as the class 47 in blue. There would then need to be a large logo version and, probably, InterCity (executive), Intercity (swallow), railfreight and RES versions, as well, I imagine, as some post-privitisaition liveries such as Virgin, FGW and all the other liveries carried by the class 47, although the sectorisation and privitisation era liveries have not been done on other locomotives or yet, either, so can possibly wait.
On the subject of liveries, the class 41 could probably do with a BR blue livery on the assumption that, had it not been non-standard, it may very well have lasted into the era when that livery was universally applied, as there was nothing particularly wrong with it aside from being obsolete before it was ever produced.