All new tooling of the ubiquitous Black 5 and 8F would seem sensible, the Black 5 in particular has almost no provision for the many variations inflicted on this design. Scope for a competitor to milk Hornby's cash cows?
Gresley's Doncaster team was so very right when it came to the essentials of the pacific design. All the successful subsequent UK pacifics are heavily influenced by that lead, and Thompson was ill advised to discard so much that was well proven, and thereby quite unnecessarily introduced weaknesses in the frame in consequence. And very quickly after Thompson's retirement Pepp proved with the A1 and A2, that Thompson's programme of independent valve gear for each cylinder was fully possible within the established frame layout. So, a false step. (The established process of developments of pre-group classes that continued under Thompson was sensible; in particular the B16/3 and O4/8 and O1 built on what had gone before. As for the B1, it supplies very funny reading in the BR exchange trials, as various commentators try to understand how the significantly more expensive Belpaire firebox taper boilered religion failed to deliver the expected superior performance.)Going back a bit ref 'Gresley was right'