There was something extremely odd about the Trojan engine although I've no idea what it was now if I ever knew.
I'm sure I read once that somebody did a technical appraisal and concluded that the only way it could possibly have worked was if the crankshaft actually bent on every revolution.
The Javelin engine was certainly a flat-four so I imagine that as it was a small company with limited resources, any vans, prototype or otherwise, would probably have used the same engine.
My Dad came close to buying a Javelin too in, I guess, the early '60s but didn't for some reason.