TD, You are absolutely correct about MSP not being compatible with 108" which includes the J.
That said there was a design that goes back to around 2001 to fit extensions. Never got into service. However it did get off the ground as was dropped from a K one time only.
As for Type V - I am not sure what the latest is in the UK these days. We did mess with the Indero Siren GRP over Wood frame filed with foam with extrusions down the sides a bit like Type V. These were 108 x 70 and could be linked. I think this is what is being used on A400M for time being. TT will know for sure.