A: It depends what year the head and block are. Later blocks are wider and don't need sealing. Measure the width of the 4.0L the head comes from and measure the block of the 4.2L before putting the head on. Subject: Re: $.0 heads on a 258 Message-ID: <20050708.140942.1140.0.superglider@xxxxxxxx> From: Wayne E LaMothe <superglider@xxxxxxxx> "They" say that some of the 4.0 heads will work without having to fill water passages and then some will have a leakage issue and need the holes filled. I do not know the difference in the 4.0 heads but it should be a point of caution. When I do the SX/4 I am going to have mine filled just to be sure. YMMV Wayne Wayne and Lisa, Bolton Landing, NY, http://web.vplp.net/~superglider/