I'll be measuring up an NV3550 over the weekend.
I've come to the conclusion that's a much better choice than the T5. The NV3550 has a 300 ftlbs torque rating while the T5 is rated for 240 ftlbs.
According to Novak, the length of the 3550 is ~1.5" longer than the T5 without its bellhousing. I'll have to measure up the T5 parts to see how the lengths compare with the bellhousing.
The Novak website is extremely biased toward the products they sell. It's also very incomplete. Do not trust it fully.
Overall length, front of the bellhousing to the transfer case face:
NV3550 (also AX15 and NSG370)= 24"
T5= 21' 3/4"
TF998= 22-3/8" (Automatic Eagles)
You'll be amazed at the difference in weight and girth between an NV3550 and a T5. The T5 is a car transmission. The NV3550 is a truck transmission. Unfortunately this translates to a very clunky, stiff shifting experience. The gears are considerably heavier and stronger in the NV3550 and you can tell. The T5 is very smooth and fast. Also beware of the fluid issues with NV3550s. They need special fluid or their synchros degrade and it will shift terribly.
I suggest the AX15. It is just as large as the NV3550 and very close in strength. It is a considerable upgrade over the T5, however it shifts just as smooth and as quickly as the T5.
Both an AX15 and the NV3550 can be mounted behind a T5 bellhousing utilizing 258 shift hardware and the thicker 258 flywheel. To do this you need the Advanced Adaptors kit. It's listed for the NV3550 but it actually works for the AX15 with a very minor modification.
If you want to use the thinner 4.0 flywheel and bellhousing, which is a great idea if you want to fuel inject, then you'll need an advanced adaptors kit to convert your NV3550 slave to metal flare line. Alternatively an early AX15 has in internal slave that is already 3/16" flare line compatible with your Eagle clutch master cylinder.