In reply to # 1447228 by CaLaxly Thank you for the advice, I have looked it up and it fine if I did a swap since I don't need to pay attention to ERC rules. I heard the 3 speed transmissions are actually pretty crud, do correct me if I'm wrong.
Certainly by today's standards they are crude. They were 3 speed, rear wheel drive automatics, derived from a design that originated in the 60s. No lockup torque converter, so the fuel economy is not very good, and no overdrive in top gear. They were made with aluminum cases, so they are not as heavy as the iron cased versions. Some TR8s used the BW Type 66, but most used the Type 65. The Stag and the Rover 3500 (among many others) used this gearbox.
There certainly are much better choices, but of course going with the original transmission minimizes fitment and fabrication issues. You will need a different center console if you go with the automatic, among many other differences vs. a 5 speed.
1980 Platinum Metallic TR8, navy blue interior
Bare metal respray, Crower cam, raised compression
ported heads, modified Zenith carbs, 0.060" overbore