Not 100% sure but I believe one bush had a "cut out" in it as mentioned by Jeff, while the other was solid. From all that I have read it is better to use the solid bush & that seems to be what all the suppliers now list as ULC1580, for both ends of the arm.
The bush is the same as the Dolomite bush 149827, the well known Hurdwell memo about suspension changes to the development TR8 mentions that the windowed bush in the rear link was replaced with 149827 to reduce axle tramp & rear wheel steer.
There is a seller on eBay at the moment listing 4 x ULC1579, new old stock, but he wants £20 each for them.
Tony
<font size="1">1981 TR7 FHC Cavalry Blue
1980 TR7V8 DHC Jaguar Regency Red - sadly sold!
1977 TR8 FHC EFI Factory development car Inca Yellow</font id="size1">