ERF-NGC-European:
There are at least three categories of relevant retro-fit:(a) Factory retrofit before vehicle leaves the premises
(b) Dealer retrofit with full support of manufacturer
(c) Later retro-fit by operatorWouldn’t an (a) or (b) retrofit surely count as a fully legitimate ‘count’? It matters little that no 8LXB was officially offered as an option in the brochures (if that is indeed the case), as brochures should reflect real-life practice, not dictate company policy. A point to chew on!
Ironically I think we’ve got evidence that the factory did publicise the option.
I’d guess that then met the reality of NA engines becoming obsolete in the eyes of some operators while many of the remaining die hards just went for the easy option of 6LXB or NA ■■■■■■■ and maybe RR.
If the unfinished vehicle never left the factory what would have been the point of any ‘retro fit’.It’s not leaving the factory so why bother fitting it with the wrong spec needing retro fit to put right ?.
As for (b) and (c) whatever their provenence they obviously wouldn’t have been factory built 8LXB Big J’s ?.
To be fair I think Bewick’s case hinges on the question of just how bad/difficult 8 LXB engine supplies really were regards Guy Motors.Combined with how many of its customers would have said it has to be that motor in it or nothing obviously then resulting in the question of would it have been (a), (b) or (c) being the logical solution to that.
Assuming the worse case supply scenario then (b) and more likely (c) seems the logical conclusion .
While assuming that issue wasn’t as bad as being suggested then I’d guess that (a), obviously with no need for any retro fit, sounds crdible.
Subject to seeing those build sheets without having to pay 50 quid 
each for the privilege. 