depends on who interprets the rules at the time. For example my shell was purchased from DJM as a brand new rally shell from them and the VOSA fool was happy to accept that as well as the supposed puma suspension and steering.

Its open to interpretation for example IMTEC built cossie pumas and sold kits and they used what was clearly modified ford shells (albeit new) but got away with selling them on as new "unmodified" shells. Hence all IMTECs should have IMTEC on the log book as manufacturer although in practice that doesnt happen a lot.

anything other than a brand new shell should be q plate though.

So yes, the majority of cossie convertions would need both an IVA AND end up on a Q plate if you went down the correct registration route.

The only way round it is to build the chassis yourself from new metal and pressings a bit like AG did. But then you have to be careful about doing it all yourself to count as an amatuer build if you follow the kit car route.

The whole thing is open to massive interpretation though, even these days. For example, on kit cars there is the issue of donor parts. Only a chassis and engine are uniquely identifiable and most ditch the chassis, so there is no way a VOSA inspector or anyone can prove if the steering, axles, suspension and gearbox came from the same car other than youre word and a few cursory photos they ask for these days. Hence why a lot of the older kit cars used a single donor for everything except engine, eg sierra/jag donor parts on cobra replicas.

Anything fancy, people tend to go the all new parts route with a recon engine to get new reg.