I think the general consensus is for the #7120 head as the preferred swap. The flow characteristics of 0331 head were reduced somewhat to achieve better emissions. Now I'm sure someone will come along and disagree. This link has all kinds of data on the various versions of the 4.0 thru the years. http://jeep4.0performance.4mg.com/tech_specs.html
I don't think a new head has any particular advantages over a properly tested and re-built head.
edit: I've heard/read that the 0630 heads were more prone to cracking. Haven't heard/read that about the 7120's as hinted at in your e-bay link. I would ask Titan what they mean by re-machining?