Superman,
The 924 nor the 944 were designed by VW. Like you said, Porsche did use a lot of VW parts in these designs, and funny enough, VW parts are almost always cheaper through Porsche, sometimes less than half the price, A 914 case costs less than half of what VW charges for a mid seventies Type 4 case. All of the 477 and 478 partnumbers are Porsche as well, though I believe the 477/478 numbering system was aimed towards use in the VW organisation at first, and I can't help to see the link with Type 4 here .. partnumbertechnically speaking then .. (new word?!)
The idea was to have VW market (what became) the 924, and Porsche would have a source for cheap bodies for the more upmarket 944. VW had a change in management, and found they really didn't need the 924. Porsche almost saw all of their hard work go down the drain and then decided they would have to produce and market both models under the Porsche name, they struck a deal with VW ( money, fancy dinners, maybe a 'business' trip to Amsterdam..
) to use the Neckarsulm Audi plant for this purpose. The galvanising equipment for the bodies was put there by Porsche and is also one of the main reasons that Audi started to galvanise their bodies (I think) .. because the stuff was just sitting there .. ( I wonder if they would let me use it ..)
I am still not 100% sure that the 924 really had an Audi engine, because I think it is much closer to a VW LT engine .. but then .. who cares .. because that is about as much as saying "Hey .. that is not a T1 case .. its a T3 case!! Dangit! " ..
For the 1986 model year the 924 got a "real" Porsche engine (sorry about that .. I know, a reall Porsche engine is not watercooled .. ) .. the 2 liter was tossed in favor of the 2.5L from the 944s, and it became the 924-S. I've driven one of these for a while and it's actually faster than an early 944, nice ones can be found cheap, it's a nice car to play with, they're still ugly, but anyway .. The 944s never had a VW engine though, always a Porsche designed 4 cylinder in either 2.5, 2.7 or 3.0 liter with or without Turbo and/or some extra valves.
Thanks for letting me ramble
Brian