Right out of the HD parts book on the motor .... its a 107. SE259E cams is the same cam used in a SE 110 engine set up. Also the 120R has MVA heads. Its not the same motor. If it was (102ST) it would not produce the same numbers nor would it come with a 1 year warranty. Its a marketing game for HD suckers. Stop by the parts department next time your there and ask for the spec sheet on the 107... One really doesn't exist. There is a glossy page with some minor details on the setup. You will have to go down to the small print to see what it actually is.
That statement is completely false. Both the R and the ST share the same 4.625x4.060 configuration both with the save MVA heads. The only performance difference are the cams. The R has 266s and the ST had 259s. The ST also comes with the screamin eagle 58mm throttle body and 5.3 injectors. IMO the ST is a much better deal because it comes with a cam much better suited to the compression of the engine and the throttle body. A 107 can make the numbers that the 120 makes but it will be very high strung and will have to be very well tuned. The 120st is a great touring option along with a Fuel Moto E-Zilla would make a great long distance hot rod that is not hard to tune and fuel friendly. My opinion comes from building and tuning both not from being an internet forum builder.