@ inetdog Thanks for pointing out (what should have been) the blindingly obvious.....apart from a bit of heat-insulation in between the cells, they've simply "bunded" the original design enclosure...albeit they'll have to have made it bigger to allow for the increased bulk/spacing of the individual cells.
What a clever idea to keep it looking just like the old one
now we wait till an old-type gets fitted by mistake.... but hopefully the reinforced firebox Bund has been designed so the old units don't fit in, so eliminating that possibility.