Why do you need a new X member?
IIRC, from the BA10 to AW4 swap I did on my 2nd XJ, all I had to do is move the stock X member back....or was if forward? Either way, if you look at the unirail where the X member bolts on, there will be 3 holes, which allow you to shift the X member forward or back, depending on your tranny type/length.