That’s interesting about the shim: a quick/cheap way to solve the matter. However, I think the matter of the trailing/leading link is more complex than just one mark vs another. There was a thread on Britmodeller.com (sorry, but I didn’t keep it) dealing with precisely this. From memory (please don’t rely upon this!) the changeover occured partway through the Mk.VIII production line, so presumably partway through the Mk.IX too. The thread did quote different part numbers for the different oleos.

PS it may have been a thread here rather than Britmodeller: look perhaps for references to Aussie Mk.VIIIs?