I agree with what you say, it may be the question of who welds it. When I was racing my E Type I had some work like this done by guys that built race cars - not on the output shaft but on shortening the half shafts, which were forged. I was putting 375 and 335 ft pounds of torque through them and running on racing tires with significantly more grip, and a uprated limited slip diff. The half shafts had a bit thicker shaft than the output shaft. Ran for years without issue.
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Driven Man are never in stock. They say 3 months, but in reality way longer. I waited 6 months and was told, we have no idea when it will be shipped. I then canceled my order. They kept a $150 deposit for cancelation.
And I suspect that the weld penetration was greater than the circa 3-4mm that’s typical of TDM part.
The guy in the following video does a better job than TDM, where his weld prep allows for weld penetration right down to the core, with each weld bead refining the previous.
Hello Tim.
They’re never wrong. 
Regards,
Bill
The more I wait the more I realize lots of these upgrades are bogus
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Hi Keith
Yea iam the guy that put 5 speed from driven man in my customers car. I had such a time with Robert. If you buy there product dont expect any help with problems. Missing parts, wrong parts etc. Look at my post from a few months ago, it will spell it out.
If you go Guy Brand you can also expect the worst. I would tell you more but my customer holds out some hope of restitution Its been over a year and a half. No luck!
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Hi Mike
I am sending you a PM.
Someone else made the point, but I’d like to put in a vote for changing the rear end to a 3.07:1 (or thereabouts) is way less expensive, and with a standard Jaguar 4 speed makes the car much more relaxed on the highway.
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We have put 2.88 in a bunch of cars and they work great.
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From what I’ve observed from this site I would never install one of these 5 speeds and I have all the skills. Way to many hassles and poor support
Just change the diff gears
My vote
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Thanks for the response. Getting everyone’s input is invaluable to help me decide what to do. Part of my reasoning for installing the 5 speed is because I have to replace the front seal on my transmission so I figured since I will drop the engine out I may as well upgrade. Now I’m not so sure. I also like the idea of changing the rear end since I have a 3.54 .
You’ll spend less money, and you’ll will stick with a transmission that’s tried and true.
No downside there!
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Good idea that I have not considered.
Good to know
Keith
Where do you get a 2.88 for a 3.8 liter Jag?
Keith
It usually starts with something like that.
The rear axle in your Jag is a minor variant of a Dana 44, as found on Jeeps and pickup trucks. The variations are the ring bolts (which will need to be sleeved) and the input flange. You may find that you need some shims. From time to time, there are flanges available (pn may be Spicer 2-1-2391), or you could just use a Chevy yoke (Spicer 2-4-8091X) . Using Dana 44 gears gives you more choices, greater availability and lower cost. They’re widely produced in the aftermarket. Here’s an article about the Dana:
https://www.hemmings.com/stories/article/dana-44-differentials
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I put a 2:88 in. I live in San Francisco. I have zero desire for a 5-speed. 80 mph cruise is fine and I actually have a usable 1st gear which you don’t in a 5-speed IMHO.
Does the 2.88 rear end bolt in with no modifications?
A 2.88 on a 3.8 may be a bit too long in city traffic or if you have to climb a garage ramp, or else if you drive on steep mountain roads with sharp bends.
3.07 is probably the best compromise.
I have a 3.31 which is fine for me and avoids using too often the 1st (non synchro) gear.
You only change the ring and pinion gears and you probably will need a new yoke for the pinion. Everything else stays the same. The ring & pinion will require a skilled hand to set up.
EDIT: if you are sourcing your 2.88 gears from the salvage yard, take the differential (the thing the ring gear bolts to) too. By the book, there are only 2 basic Dana 44 differential units: 3.73 and down, and 3.92 and up. I have never seen a 2.88 gear set, so there may be some OEM variant associated with that specific gear ratio that is not a standard part.