This is precisely why I like this period as a basis for modelling. You can run steam alongside B101, B121, A, C, E401 & G601 class diesels up to the start of 1963; and while the steam disappears after that, the B141s enter stage left.
Wagons - old GSWR & GSR, with an extremely occasional DSER or MGWR type, may all be seen together wearing darker or lighter grey; the former with painted pale green or qwhite snails, latter with stencilled white snails. (No brown till a decade later). But in addition, all the new standard CIE types from Bullied opens to "H"s.
Carriages - you've old wooden stuff from GSR, GSWR, MGWR and a (very rew) ex-DSER or CBSCR in both green liveries, plus in the first three categories some in black'n'tan too. Amongst these are new CIE stock in silver, or lighter green, or black'n'tan; plus ex-GNR stock either in GNR brown, GNR navy & cream, CIE light green or black'n'tan. Add the tin vans in green, silver or black'n'tan.
At no point before or since was it possible to get a mix like that. The reality was that at the very point when motive power was changing from steam to diesel, the railway had gathered together the last few of a myriad of different types of everything, which were now being added to and gradually replaced by brand new stuff; and in the midst of all of that, the railway had five diesel loco liveries and four for carriages all at the same time, as WELL as "imported" GNR types - blue or blaxck steam engines, and two GNR liveries.
And it was not even a case of "all old carriages are green, all new ones black'n'tan". Some older vehicles, built in the 1910s or 20s, were newly turned out in black'n'tan, while a "new" coach (say, a laminate built in 1958) was still green.
A final twist to the tale with the six-wheelers. These, within that period, still held sway on a handful of branch lines, all being the lighter green by then. Early 1963 saw the end of any passenger six-wheelers, but as we know from the Hattons release, three or four six-wheel full vans remained in traffic after that, until the late 60s, and were painted black and tan, and therefore will have seen use alongside Cravens! The latter, otherwise, would never have run with any six-wheelers.
Incidentally, this is why only the six-wheel full brake is offered in black'n'tan - in green, it ran with passenger-carrying six-wheelers, but in black'n'tan it would only have run with bogie stock. No passenger 6 wheeler was repainted black'n'tan. A pity, perhaps; sheer curiosity makes me wonder what a Midland 6-wheel third would have looked like in that guise!