Found some more interesting sites but not the engine dimensions I am looking for.
As in the engine compartment or the engines themselves?
If it is the former, just measure a model and do the maths. If it is the latter do the same and half the measures for width.
I'm looking for block length for the base AEC and Leyland engines, though ideally I would like some dimensioned engineering drawing for the power packs as also for the 6046. I have now found multiple references to the AEC / Leyland power packs being the start point for the GM 6046 but no confirmation that they were the same size. May have a chat to some RAEME contacts and see if any of them can access data at the Armour Museum.
Looking at the suspension set up there are two full bogies in the middle and a half bogie at the read of each side, there is also a separately sprung wheel between the idler and first bogie, this appears to give enough space for three HVSS units on each side. The other possibility that comes to mind is using M-2/3 light tank suspension bogies, three per side, though it may not be up to the 25ton weight of the Matilda, even with the extra bogie.
An interesting comment on one of the links I provided was that fitting the 6pdr in the original turret was never attempted, though it may actually have been possible considering the Soviets fitted a 76mm.
The other thing, which is not something I had previously considered, is that apart from its armour advantage, the matilda was also much more reliable than its cruiser tank contemporaries, its only real down side was its low speed.