67 rearend width vs. jag irs

i am looking at a 1975 jaguar xj12 irs that has a 61.75" track width to put in my 1967 fastback. what is the width difference between this and the stock 8" rearend. i know its not going to be exactly the same but hopefully close enough to put spacers on it or backspace the wheels a little more. i want 18x10 or 18x9 for the rear.

dazecars has a good article on the jag irs. he had to shorten his because he put it in a 66 stang. wonder how hard that really is to do.