Hi Bob, I just noticed that I unintentionally grubbed Post 200!
Under their JT5CR box description they show a 0.90 5th gear, so I would guess they sell them separately. Give them a call. I've always learned more than I needed to know when I've talked to them. Let them know what your application is and they'll be happy to help out. Since you're not running Godzilla Horsepower, they may have a relatively inexpensive solution for you.
BTW, a lighter flywheel on the Jags really brightened them up quite a bit under power. My street Jag's flywheel is light enough that when I depress the clutch pedal, the idle drops a bit.
Best regards, Tom
Port Washington, WI 53074