Okay, it's not AMC related, but I know a lot of us AMC nuts also like 
in-line sixes and would like to see the AMC 4.0L continue in one form or 
another. The Strokers group on Yahoo Groups (specifically for 4.0L engines 
w/258 cranks) has mentioned things like cross flow heads an overhead cams 
as possible improvements. Then Chevy came out with the Vortec I-6 as their 
new truck engine. It has variable timing, and the I-6 is a cost saving 
package for that. With a V engine four cam adjust mechanisms are needed, 
with the in-line only two (or one if only intake or exhaust is variable).
Well, Ford apparently didn't take that lying down! Ford of Australia 
released a 24 valve DOHC 4.0L in-line six in 2004, in the popular Aussie 
Falcon! That's the successor of the car Mad Max used. Chrysler even had a 
hemi in-line six "down under", those guys apparently appreciate a good 
in-line six banger!!
Here's a link for more info: 
http://autoweb.drive.com.au/cms/A_55206/newsarticle.html
--
Frank Swygert
Publisher, "American Independent
Magazine" (AIM)
For all AMC enthusiasts
http://farna.home.att.net/AIM.html
(free download available!)