Jes is correct it is a standard Spicer part and you can get it from anyone who sells Spicer. The price is that same from anyone else when i looked so i saved myself the headache and run around and got it from RE. BTW. I paid $60 for the H&T flange without hardware. I just used grade 8 bolts from Home Depot and already had the tap.
There is no issue with the strength of the XJ front shaft. You need to check the length if you are running a lift >4.5". The strength would be an issue if you are running something other then the stock engine and drive train. (Hot V8, big axles) Then i would look into something custom. I have bene running this set up for 2 years with NO issues. Just did Tellico this past weekend again with no issues.
Mike.