The T-56 is a legendary transmission in the 3800 world. This transmission is known for being nearly bullet-proof in stock form and offers plenty of aftermarket support. There are few who have done this swap though still.

The T-56 is a 6 speed manual longitudinal transmission. It was the standard transmission behind a lot of LS-based V8 engines. You can find this in Camaro's, CTS's, Corvette's, and many other RWD performance cars from GM.

Because of its demand it is hard to find one without investing a significant amount of money. However compared to the cost to build a 4t65e today, this cost is pretty insignificant.
You can have a 700ft lb rated T56 Magnum behind a 3800 with less than $5,000 invested into the swap depending on the application.

The factory T-56 is rated to handle at least 450 ft-lbs of torque in the 98-02 f-body's. There are countless examples of people who have pushed this transmission well beyond this range you can find online.

There is also the option of using a T56 Magnum or TR6060 as well and these are rated much higher. The magnum is rated for 700 ft-lbs of torque and the TR6060 is rated for 600 ft-lbs.

Of course there are lots of examples of people using these transmissions with over 1,000 ft-lbs of torque without issue.
In general these transmissions are considered bulletproof unless it is being abused or if it has a lot of miles on it.

Use this information at your own risk, this may be incomplete or lacking in some areas

You will need to use an adapter plate to make this transmission fit your car. In the US you will need to look at the aftermarket for such an adapter plate. In Australia it seems like there is an OEM bellhousing that will bolt up to both the 3800 and the t56.

The aftermarket adapter plates would either be installed on the bellhousing or the mid-plate of the transmission depending on what route you choose to go down. If you use a mid-plate adapter you allegedly could use the f-body t5/3800 T5 clutch and a early 90's/late 80's v6 bellhousing for an option that nearly bolts together. The earlier bellhousing is required because the 3800/T5 bellhousing uses the Ford style bolt pattern on the T5 instead of the classical T5/Muncie pattern. The mid-plate adapter uses the classical T5/Muncie pattern instead of the Ford pattern.
You could potentially create your own adapter with 1/2“ thick aluminum, but you'll want to make sure your bolt holes line up absolutely perfectly.

Again, you will need to do your homework though here. This has not been documented very well yet.

The other option is to use the LS style bellhousing and an adapter plate between the bellhousing and the engine.
Malwood appears to make an adapter plate that will work: https://malwoodauto.com.au/product/adapter-plate-kit-for-holden-v6-to-suit-ls1-t56/
This gives you the option of using any LS T56 you want to including the Magnum T56 and would also give you a larger bellhousing with more potential for larger clutches.

It appears that you can use the factory style 3800/T5 clutch because the spline count is the same between the T56 and the T5 used in the 3800s.

You will also use the 3800/T5 or LS/T56 hydraulic slave cylinder (both are the same)
The slave cylinder will need about a 1” spacer between it and the transmission to make up for the space used by the adapter plate.

Some sites recommend using an adjustable clutch master cylinder as well.

The OEM 3800 pilot bearing sounds like it would work with this swap.

You will need a few wiring pigtails:
- Reverse lockout harness pigtail (ACDelco 12101857)
- Reverse lights pigtail (ACDelco 12085485)

You will also need to consider the vehicle it is going into for things like your driveshaft slip yoke spline count, what master cylinder you're using, how long your clutch line needs to be, and any other wires that need to be added. The transmission mount will also need to be modified as well, or a different crossmember might be needed.

If you're going down this route though you probably have a pretty good idea of what you're getting into already.

Other sources to look at:

https://www.thechicagogarage.com/threads/3800-t56-swap-guide.177394/

https://forums.justcommodores.com.au/threads/vt-v6-6-speed.229878/

Cost