Cool find, yep there was one kit that maintained the stock intake manifold, but added a sandwich plate between it and the head. At first glance, you wouldn't know it would be turbocharged, eh?
I have somewhere in my paper archives, some copies of magazine articles showing various 1.5l aftermarket turbo-add on kits, which were popular before VW introduced the factory-turbocharged 1.6lTD. If someone needs more information on something particular about one or more, let me know and I may be able to find something useful in them for ya.