In the reprinted (~late 70s) summer edition of Ian Allen's Locomotve & Locoshed book 1959, D8046 is listed but there is no shed allocation information which suggests that it was built during that year.
The allocations for D8000 to D8019 are either 5B (Crewe South) or 1D (Devons Road)
That's the only "green" information I have.
In the 1973 edition, all 3 are still on the list but have been renumbered in the 20xxx series.
They are still in the list in the 1979 edition - none were fitted with dual brakes.
The shed allocations in the 70s were as
follows:-
1976, 1977 20 046 - ED; 20 113 - TO; 20 134 - TO
1979 20 046 - ED; 20 113 - TO; 20 134 - ER
ED = Eastfield (Glasgow - 65A)
TO = Toton (16A)
ER = Typo / misprint???
David