Picked up two Centurion Lemans - a Lemans 12 and a Lemans RS - a couple of weeks ago. One was a basket, the other was nearly road-worthy. Never mind. I've torn them both down to the frames and will take them in for new paint next week.

Stripped of all but their headset bearing races, I weighed each frame individually. Results are shown below:

Lemans RS, serial no. N5G6351, frame decal says Tange 2: 5 lbs 3 oz., (2.34 kg).

Lemans 12, serial no. N4H5314, frame decal says Tange 900: 5 lbs 5 oz., (2.42 kg).

So very little difference between the 2 frame types. Although I haven't measured yet, visually the frames appear identical in every dimension.

EDIT: Corrected units, see above.