avnsteve said:check head casting number, that year model had a problem with heads cracking, do a quick search for something like "2000 year cracked head" there is much discussion about which should help you reach a decision, other than that, the 4.0 is pretty bullet proof and you can hardly go wrong. post back with your findings and/or do your search. I had a similar decision to make and found the help i needed with a brief search here
mtsz52784 said:just search 0331 head... you do not want an xj with a 0331 head because you run a 50% chance of the head going to crack. you really want a 4.0 from 99 and older and you'll be all set. i bought my 2000 xj and just reached 70000 and the head is cracked so now going to fit it with a 0630 head and exhaust poort adapter so i only have to change the head.
mtsz52784 said:the last of the xj's (2000 & 2001) have the 0331 head... the exhaust port adapter isnt something you can buy, but has to be made from a machine shop, and is something to help the bigger ports size down to the 0331. go to the top and search about 0331 head or cracked 0331