In fact, looking at the pictures, I think the solution is very simple. Make roof projector light unmountable module. Move roof rack a few cm forward replacing roof projector light (it has extra lamps on the roof rack anyway). There is enough space for it.
But for "gaswagen pipe", probably some module conflict mechanism should be used, like we already cannot have long snorkel and cabin cage on this truck.
Please make big round air filter on the van body (kung) 1 unit (see picture). It will allow to use at least one custom exhaust pipe (on the left side) and it will fit van body relatively well.
Also move roof rack a bit forward and make it conflicting with projector, not with van body as I showed on the picture above. Anyway there are extra lights on roof rack.