The engine number is quite a b**ch to see on them. The dipstick will have a white dot on it, but only if it has the williams sump too. A normal valver came with either a black or blue dot on the top of the dipstick.
The best way would be to drive it, if the engine is just a valver one, you won't notice that much below about 4k revs. A willy engine has more low down torque, so you should notice that.
If it's got a williams gearbox too, it won't hit 60 in second gear at all (top is around 57 mph) a valver engine & gearbow will hit 60 in second.
I believe (don't quote me on this) that the rev limiter is a bit lower on the williams, but if would depend on the ecu it was running.
Matbrown & Winston etc, will be able to tell you more (if there is more) they will also say my info isn't totally accurate
