Thank you to everyone who offered valuable advice. I went to the auto parts chain this morning and they had the special tool specifically for hose clamps (3/8 & 1/4) for $10. It doesn't seem as bendy as Grant's, but it was valuable for getting this job done (Thanks Grant!). You'll also find long reach needle nose and hose pliers handy because you might squeeze one hand or few fingers where you need them but you'll need the pliers or a long screwdriver to hold or move something.

I'd rather not do that job anytime soon, as that lower LH hose is a female dog. I'd love to see the factory production sequence because either they put that in before the engine or there is a special gnome at the factory who has long super skinny, but strong arms, that can reach in there. My wife and daughter were horrified when I came inside and my arms were a bloody and greasy mess.

Here are my tips:

I not only had to remove the balance pipe, but also the top portion of the throttle pedestal. Once you have the top ignition coil bracket off and set aside, you have a good angle onto the LH clip on the heater valve.

It helps to take the little hose disconnected from the balance pipe, and move it as far over toward the LH fender as you can threading it amongst the wires etc., to help get the hose out.

To snake the new hose into place forget about the hose clamps and just do the hose itself, wiggle it approximately in place and temporarily attach it to the heater valve.

Then thread the heater core end through everything and move the balance pipe hose back to where it belongs (easier said than done).

Slip the hose clamp on and attach to the heater core (again easier said than done, but just be patient).

Once that one is tightened up pull the hose off heater valve and slide the clamp on and reconnect. I normally put the clamps on before putting the hoses into place, but with this one you'll either not be able fish the hose where it needs to go or you be dropping a clamp somewhere you might not be able retrieve easily (don't ask me how I know).

Once I had everything back together, I followed Grant's method for filling/bleeding including opening a fresh cold beer to make sure I went slowly on the fill. Really slowly add no more than quart, let it gurgle while you take a sip of beer then start putting a few tools away. Another quart, sip beer, clean up, repeat. By the time you have the system filled and all the air bled, the garage is cleaned up and the tools are put away and beer is empty.

Final note, the thermostats I removed, which I'm almost certain are the original factory ones are too short to fully close the bypass. I had earlier speculated that maybe it was an intentional engineering kludge for some reason like emissions or mileage restrictions, and why the 'latest' Jaguar part numbers are the wrong dimension. I'd rather have the system work properly and keep its cool rather than squeeze out a tiny margin trying to meet gov't regs.

 

Good job done.

AND YES

Engine out is the easiest for many things on a V12. Usually about 6 hours, out on the ground, think about it. I did, and thats what I do now, sounds dumb, is not.

That A/C TX valve, buried back there IS an engine out or the risk of cracking/snapping the evaporator tube is in the high 90% range.

This is where the phrase I use comes from:

"Do it ALL, do it properly, repeat in 20 years".

 

I have a feeling your 6 hours would turnout to be two full weekends for me... haha

 

Took the beast out for an extended test drive and to get it out on the highway. I'm actually taken aback by what a difference the thermostats make. My factory installed stats were 87C and the shorter dimension that doesn't fully close the bypass, and replaced with 82C and the proper length. Before, on a day like today (85F) once up to temp the needle would point to the bottom of 'N', With the new stats, the needle sat below the 'N' and never reached the old level.

Before I ordered the thermostats, which were offered in three different temps (77C, 82C and 87C) I wrote Roger Bywater and asked him his thoughts:

"V12 thermostats were changed from 82 to 88 in about 1977 mainly to improve fuel efficiency and emissions.
There is no benefit running at a lower temperature, in fact running less than 82 can cause problems by provoking excessive acceleration enrichment.
Thermostats only control the minimum operating temperature and make no difference if an engine starts to overheat. If a V12 overheats it is because there is something wrong that needs to be put right."

I found another source who stated that the ideal horsepower temp zone was 82C. I'm happy to trade a little fuel economy (heck, I bought a V12 not a Prius) for horsepower and a better margin of safety on the cooling front.

It's all very interesting,