I installed a kit in 2002 in my 90 XJS conv. 5.3 liter. The kit is actually engineered by Keisler Engineering. The Driven Man is the sole distributer. Robert Hall is the contact there at Driven Man.
I happen to like the kit. The original slave cylinder from McCleod engineering had a lot of problems with clutch dust getting in the orings and causing leaks. I was having to pull the transmission every 12 - 18 months to change the orings. That got real old.
The kit currently uses a slave cylinder that is european and has a dust boot. I think this slave cylinder is much better engineered. I have had it for only about 6 months, so I can't say if the leaks are completely solved.
Two things that are very important. First is that you need to use a plumber's wire brush (for cleaning copper pipe before solder joints are made) to clean out the boss in the rear of the crank shaft. Do not try to substitute a gun bore cleaning brush. It is not stiff enough. If the pilot bushing does not just slide in to the crank with light finger pressure, remove it and clean the boss some more.
If you drive the bushing in place with a drift, there will be enough compression of the bushing to cause it to bind on the transmission pilot shaft. The bind will be great enough to preload the crank forward against the crank thrust washer and the engine will seize!
"Been there and done that"! Trust me on that.
You want to pull the EFI fuel injection ECU from the trunk and send it in when you order the kit. Keisler will reprogram the ECU to shut off fuel flow when you shift gears. This will prevent backfiring from the exhaust if you hard accellerate and change gears. If you wait until the installation is complete to send in the ecu, you will end up waiting quite a while to get it back. Took me 5 weeks, but that is just the experience that I had. They might return yours sooner.
I have some other posts including pictures of the new style slave cylinder that pertain to the 5 speed kit. If you are interested look back to see them.
The Tremec 550 or 600 TKO transmission weighs about 125 pounds. Although a lot of work, I removed the engine and installed the engine and transmission as a unit. It can be done from underneath, but the older I get the harder it is to lift that transmission and stab the rear of ther crank with it. I tried several times over several nights before deciding that life was too short and just pulled the engine.
I installed the five speed Kit. I can cruise around in 5th gear all day just above idle at 35 - 40 mph at 25 miles to the gallon. I get about 22 - 25 at 70 mph highway.
The advice I suggest if you do a lot of highway driving is to consider the six speed kit. I think that you could do better on the highway with your fuel economy.
Again, I like the kit a lot.
You might also check out Vintage Jag.com Walt Osborn also has a 5 speed kit. You might want to comparison shop.
Good luck.
Hey there Guest!
Hey - did you know if you click on the title of a thread it will take you to the first unread post since you last visited that thread?
but were afraid to ask: 
STOP!! Never post your email address in open forums. Bots can "harvest" your email! If you must share your email use a Private Message or use the 
smilie in place of the real @
Pretty Please - add it to our Events forum(s) and add to the calendar! >> 
A friendly reminder - be careful what links you click on here. If a link is posted by someone you don't know, or the URL looks fishy, DON'T CLICK. Spammers sometimes post links that lead to sites that can infect your computer, so be mindful what you click.