oil filter adapter

I have a 97 w/ 4.0 and 158k. While doing my last oil change I noticed a seepage leak at the oil filter adapter where it bolts to the block. So my question is, does anyone know how long the bolt is? The exhaust manifold happens to end there, and i have about 3/4" to get that bolt out. Dealer has no spec on the bolt. Any help would be appreciated.