You failed to specify a year. Now let us continue.
Triumph T120 Circa 1969 380° crank. 650cc displacement. Triumphs are known for their bad balancing.
BMW R-60/2 Circa 60's 180° Crank 180° Bank, well balanced, and shaft driven.
They sound 'similar' but the difference in the exhaust, and drive type results in different noises. If we put the SAME exhaust system on both engines, they would sound even more similar with small mechanical differences between the BMW having twice the chain in the engine, and the Triumph having a poorly balanced crankshaft.