Free speculation it is then!
Four engines, the second from the right of the illustration is half merged with another structure (tailcone? fuselage? dorsal something?)
I was asking myself wether it was super- or hyper-sonic, but you question makes even more sense to me, Reg.
Also, right wing (to the left of the picture) seems a compound delta, whilst the left (the one to the right) seems like a simple cropped delta, but it might just be a trick played by the silhouette: I think it's compound, after all.
And another thing, the curve of the back of the plane is quite marked, and the plane itself seems to get pretty thin after the wing LE.