Hi Karl,
As far as I am aware, only the XJ and XJS and possibly Mk10\420G used that particular top cover, Mk2, E Type, S Type, 420 all used the shorter extension. That said, there should be a few around; I do recall someone on this site saying they had several 'boxes the same as mine, plus all the overdrive ones will be the same ( for XJ6 that is) Maybe ask on this thread or place a classified wanted ad, there are bound to be 'boxes that are internally stuffed that someone will be prepared to separate.
Good luck.
PS Not a great shot, but this shows the short top cover as fitted to a 240, but same as the other mentioned models. Also looks like it might be used on the Mk10.
You should be able to do a straight swap. The etype crowd are far more plentiful and likely to want the short top covers much more than the xj12/xjs crowd want the long cover.
Incorrect based on my personal experience. Additionally, companies like V12 Jaguar Bell Housing (Metatronic or something like that) and QuickTime who make v12 bellhousing only make a single bellhousing for all v12s.
Some v12s will have no dowel pins so you’ll have to install them, but the holes are there.
