If these are the same ones you had at the GTG we found this on the inside of the wheel on the hub I think. 16 X 8 and 16MM. No name, and not ET or E or anything else for that matter.
Charlie, maybe the 16MM is the offset.
My rims measure 8" (from outside of rim on the outside to the outside of rim on the inside) which would put the physical center of the rim at 4" from either edge.
]--------.--------[ rim = 8" overall
l--------4--------l so center (no offset) would have the hub flat at 4"
On my rims, the outside edge to the flat of the wheel hub measures 2.5".
Since the physical center of the rim is at 4" then by subtracting where the hub flat actually is (2.5") from the 4" physical center gives us a value of 1.5" which is the offset from true center.
This is a positive or plus offset. If the hub flat was offset towards the center of the car then it would be a negative or minus offset.
]----h---.--------[ my actual rim with hub flat 'h' offset towards outside of the rim
l----2.5--.--------l measure from outside of rim to flat of hub
4" minus 2.5" = 1.5" which equates to an offset (expressed in mm) of approx. 38mm.
If Rollguy's offset is 16mm then the hub flat on his rims should be offset 5/8 of an inch towards the outside of the rim from dead center. Then again, maybe the rims are different sizes and different offsets.
Get a tape measure and measure the rims rollguy.
If I have "splained" this wrong someone please correct me and put me out of my misery.