One thing I love to do at my age (75 ) is share with others the things and tricks I’ve learned.
I’m sorry if I come across as a grumpy curmudgeon. I honestly don’t intend that.

 

All that is needed to show the real beauty of the engine is careful movement and dressing of the engine. The alternator is far too massive for the required amperage. The power steering pump can easily be replaced with a pump body only with a remote reservoir. Making room to move the A/C compressor out of the V clearing that whole area of a mess. With the later 6.0 eliminate the coil packs by using coil over plugs and again cleaning up the engine. The injector rails are far too bulky and complex. Use something like the rails for the Atlas 4200 engine. The throttle bodies can be replaced by the throttle bodies of the 6 cylinder 4.0 to gain added power potential and a simpler cleaner unit.
OK it will no longer look original. However now it will look like something Sir Lyons would put his personal stamp of approval

 

Yes I have a unisyn, but it's also dealing with non original carbs with wrong needles, linkage that was made to work and also isn't original (or the same length side to side) and a whole host of other things. Tuning and balancing a set of original triple SU's on a 3.8 or 4.2 E Type is easy for me, this particular V12 isn't playing nice.

 

That makes a lot of sense. Now I understand your difficulty. I assume you’re trying to use a selection of carbs?
The SU guy in New York ( (name escapes me right now ) makes it easy but more expensive. He can sell you new correct needles and linkage parts. Joe Curto 718-762-7878

I dealt with the same thing, using 3 HD8’s from a MK 10 and a 4th from a Rover 2000. Once I sorted out the differences. Then using E85. My first attempt was to use the same UO needles and simply increase the jet by 20%.
Eventually I realized my problem wasn’t the carbs. But the distributor. The HE has a wildly different curve and vacuum advance/retard than the earlier carburetor distributor. Once I sorted that out I fell victims to the seasons. Pump grade E85 is seasonally adjusted for ethanol content. It varies from 51% ethanol in the middle of the winter to 82-85 % ethanol in the heat of summer. Further compounded by fuel delivery schedule.
The solution was to order it from race fuel suppliers. That is a full 85% ethanol and a higher grade of gasoline. That brings its cost up to the price of premium. But it’s always consistent and you don’t need to worry that it’s sat in an underground storage tank too long.

 

The owner bought the SU conversion kit from Burlen, and it's a challenge to get everything working correctly. The HIF44's don't have an idle air bypass for example, so idle speed is adjusted by opening the throttle plate. That means the butterflies have to be adjusted perfectly to ensure they open in sync, yet each set of 3 cylinder doesn't draw quite the same amount of air, and then I have to compensate for the slop in the linkage. Of course access to the adjusting nuts on the linkage isn't easy, so It's very time consuming to get right.

 

Back on the original topic, in a very weird way I actually like the looks of the V12 "mess". When someone asks to see the engine, there is usually some version of "whoa!?" when they see it, followed by "you actually do the work on that?". It's kind of funny.

Since the beast will never have the looks of a polished XK engine, no matter how hard one might try, I think the "mess" is a wonderful tribute to an under-resourced engineering team trying to adapt to a rapidly changing regulatory world. For that it has its own beyond skin deep beauty.