I heard that cherokee's had problems with the I6 heads? something about they warped and were not that reliable.
Does the TJ's have the same problem with the I 6 engine?
The #0331 head did have a slight tendency to crack sometime around 130-180Kmiles. This is the "early" head, through mid-2001 - the later head with the "TUPY" foundry mark is revised to correct this.
The crack, if it happens, can be seen merely by removing the oil fill cap and looking in - it usually cracked on the upper surface, between the #3 and #4 cylinders. I am not informed as to how well stop-drilling and welding works.
The "TUPY" mark may be found in the same location, it will be raised from the surface of the head.
The cylinder head casting ID number can be found outside
the valve cover, top surface of the head, above and between the #3 and #4 exhaust ports.
The TUPY 0331 head is a direct replacement for the earlier 0331 head. Also, the 0630 and 7120 may be adapted to fit - the intake ports did not move or change very much, but the exhaust ports did reduce in size with each change. An adapter plate would be needed - use min. 1/8" thick steel (mild steel okeh,) and two exhaust gaskets - the one correct for the head goes on the head side, the one correct for the manifold on the manifold side. Open up the plate with ports matching the later
gasket with the smaller ports. Use screws 1/4" longer, get flat washers to take up the difference (retain and reuse the bowl-shaped washers directly against the manifold flanges, or replace those with true Belleville spring washers - they're there for a reason!)
The reason for this is the reduction in port size - you can actually end up seeing inside the port if you put the later exhaust on the earlier head, as the primaries won't fully cover the port.