Can not get distributor down

What is the ENGINE SIZE? .. There is a big difference in the distributors and you have MORE THAN LIKELY purchased the WRONG part .. The 5.0 L and the 5.8 L look identical BUT are NOT the same .. **Engine oil pump shafts are different size** therefore the distributors are NOT interchangeable! .. Look closely at the hexagonal oil pump drive socket on both the old distributor shaft and this new distributor shaft .. Bet you'll see the difference.