If it's a pre-unit frame, it's not supposed to have a model designation on it- just numbers. If it does, someone messed with it. You should only see model prefix on unit frames. On 50's and later Triumphs, the motor should have the same numbers as the frame, but with a model prefix (i.e. motor number TR6 020611, and frame number 020611).
Thunderbirds models were slower than the other 650 models because they had low compression and skimpy cams, but were easy to start and reliable. The Trophy 650 (TR6) had more power and only one carb to deal with. The Tiger 110 had a similar or same motor as the TR6 depending on the year, but was more of a touring model. The Bonneville was the dual carb, fastest model, but you'll spend big bucks on a pre-unit T120 motor because the Triton guys like them. You can easily take any other 650 model and install cams, high-comp pistons, and a dual carb head and make it go like a Bonnie. You're better off with the mid-50's and later big-bearing cases and a one-piece unit crank.
