Complex sentence: The R1 was only available in one spec level up to end of 2005, with one engine: the DOHC 658 cm³ 16-valve AVCS engine is the middle child in the trio of engines for the R2.
Split into simpler sentences: The R1 was only available in one spec level up to end of 2005 with one engine. A DOHC 658 cc 16-valve AVCS engine is the middle child in the trio of engines for the R2.