Well, I have known Supercars.com to sometimes make either typo errors or simply post false info, so I searched a little more. I had always thought it to be a V6, so I didn't doubt it.
My findings:
according to these two sites,
http://www.supercarcentral.com/cars/...j220/stats.htm
http://www.rapidcars.com/xj220specs.html
it is a V6, and if you convert the cubic inches on the latter, it works out to 3.5 litres (213.4 cu in).
Those throttle bodies do give a false impression, and the only recourse I can offer is this...Originally, in '88 when this was still a concept, the car featured a TT V12. However, Jaguar later opted for the lighter TT V6. So, perhaps this drawing is of the previous engine...thus, the block size and those 6 pairs of Throttle bodies would not belong to the V6. I tried to find better pics of the engine on the net, but to no avail.