The reason I'm posting this information is for anyone having to find a engine number on the 3.8 petrol motor in the Jk jeeps. I was having trouble locating the number for registration in my state. As a requirement for a roadworthy, the number must be visible to the registration authority. Until I could show its location to the roadworthy dude, no roadworthy, no registration
As he had no idea where it was, I called several DC outlets who all said: lower passenger side of engine block. But F%#&ed if I could find it. By this stage I'm starting to pull me hair out
That's until I called the boys up at Sunco Motors who went out of their way to fax me a pic of the location. It turned out to be, on the rear of the block (viewed from underneath, looking from the gearbox, towards the front of the vehicle) just below the head gasket line. It is obscured by a electrical connection, but is definitely there. DC recommend viewing this number with a mirror from the underside of the vehicle WTF! They really make it easy, don't they? Anyway, If your having trouble finding it, that's where it is.