Where did you buy it? I would take it back.
Only the spark plugs on the exhaust side of a 8 spark head ignite on the power strokes the otherside fire on the exhaust stroke. So it can easily be used instead of an 8 spark head, just make sure you hook up the right coil pack.
BUTTTTTTTT the only 4 plug head flows like crap compared to the newer 8 plug heads so you will have a loss of power and your computer may not be tuned correctly for it.
Also the ports could be different there are D shaped and round shapes for various years.
Are you sure you wasn't sold a DOHC head?
Quality Engineer (Electronics) for Kia Motors
University of Tennessee Electrical Engineering Graduate
2000 XLT 2.5L A/T