Ok, I'm playing with an 81 Spirit with a 258, and have heard about the 4.0 head swap. What special pieces do I need, or is this truly a bolt-on? Will I need a different intake and header than one for the 258? I am going with a 4bbl and header, 3.54 gears, mostly a weekend bracket car (was gonna get a 401) but will drive it every now and then in town. Is this gonna be worth it, or am I better off to keep with what I have and work on the 258 head?