Aw man, you got the hooks in me on that top pic.. Blew it up in Photoshop, and the text goes all sour when magnified. I was sure it was a testbed for the pulsejet used in the V-1.. I mean hey, look.. The thing is top-mounted just like a buzzbomb, right? Wrooooooong. It's a Ramjet indeed. The plane also is not a JU-88. Though they were used for some testing of jets, the units were slung underneath rather than top mounted. Near as I can tell, the plane is a Dornier Do 17Z with a Lorin ramjet. Check out the top photo on the linked page below, I think that's it. Most confusing to me was that at first glance, the pic you posted looked like a single-engined plane. After comparing little stuff in the pics like antenna locations and the bracing structure of the ramjet, I'm pretty confident though. Oh yea, this wasn't late war either, these tests evidently occurred from '41 on.
Info comes from:
[url]http://tanks45.tripod.com/Jets45/Histories/Do17/Do17.htm [/url]
The truck could be anything, and my bet is that the engine on it isn't even close to a production model. Looks like a proof of concept test to me.
(edited to make link hot..)