Yep! I got my valve yesterday (WED) but had a visitor here so no chance to install it yet …maybe this weekend
Give yours a suck and see if it closes and then re-opens fully when you let go the suck - mine does, but definitely not as snappy as the old jag valve, a bit lazy in fact. 
In my 89 I got 3 valves from coventry, first one didn’t leak but was pressed to hard and wouldn’t close next two closed but leaked, finally got one from rock auto (plastic) and it works great! And that pic is spot on as to the valve location.
Yup you need a vac hose,
I just changed my valve as I had no blowers on heat, I stripped 3 XJ 40s and found only one heater valve worth saving. They are out there.
You have an '89 - even new valves are “out there” - unfortunately 93/94 valves aren’t “out there”, they are just “out” 
Whats the difference, I see upto 94 on ebay?
Part number / fitting to head was changed in late cars, hose fitting one side only, not both.
This morning I took out the leaky replacement valve and installed my modification.
Here’s a dry run of the assembly with the aftermarket valve spliced into the heater hose:
Installation of my cut-and-paste plumbing was much easier than with the factory valve, and just to be sure I didn’t get a leak at the olive end I used some teflon tape on the thread.
Routing of the vacuum line was straightforward, plenty of length with no tight bends.
Also plenty of breathing space and clearance for the valve and mechanism.
Drove the car home and asked a friend to check underneath as I didn’t think I could bear seeing a leak again …anyway …to quote him, “I SEE NO DRIPS” 
Lets hope that’s it for a while!
Looks good Larry!
I’ll upload some pics after I did mine.
Hi Joe, I just went for a spin and much to my surprise, my A/C kicked in a good 10 degrees (farenheight) colder…
BONUS!!
Then you’re a happy camper.
On the way home tonight it was a bit chilly so I cranked up the heat …nice and toasty!
Larry, I installed my heater valve. In my case the vacuum diaphragm part is facing the left side fender. Here are some pictures:
Looks good Joe, obviously vacuum line was long enough, eh?
so … how does it work - nice and cold now? 
The a/c is colder now than before but I don’t think it’s as cold as it should be. I tried the heater and the air coming out of the footwell is nice and hot (hotter than before) but I don’t get hot air out of the side vents. More like slightly warm. The bend flap actuator motors worked last time when I checked them.
The vacuum line is running right in front of the valve so it’s length wasn’t a problem. Actually, I cut off like a 1/2" (12-13mm) piece because the previous valve stretched it and the connection wasn’t snug.
Joe - That ‘non-intuitive’ slider control governs the temperature of the air coming from the side vents.
Not sure if up or down increases or decreases the heat up there …I guess it’s supposed to regulate the amount of cooler air to the side vents when you have the heat cranked up to stop you from falling asleep at the wheel or something …
My A/C is down to 39, (4 celsius) so not super cold either but way better than the 50 it’s been at for the last couple of years.
From memory its supposed to be about 20 deg lower than the foot well so that you don’t reach a soporific state while driving.
Larry, Robin, thank you guys. I’ll play with that slider and measure the air at the side vents.
Ok Joe - measure the a/c at the centre vent too - I’m interested in what you’ve got coming out of there …
Alright Larry, I’ll report the results back.
