The Aurora K250 BB is just one of a wide range of model engines produced by the Aurora Model Manufacturing Co. Pvt. Ltd. of Calcutta, India (now correctly rendered as Kolkata). This company began producing model engines in 1966 with its well-known Mills .75 and 1.3 reproductions. The company's FRV series was introduced in the 1970's, with the K250 BB and K350 BB ball-race models making their initial appearances in the early 1980's. Both twin ball-race and single (inboard) ball race versions were made available.
These engines were quite recognizably based upon the old FROG 249 BB, which had been one of the more popular British engines in India. They were very successful, continuing in production for many years with a few changes along the way. I have personally used a modified example of the "middle" variant of the 2.5 cc version with great success. Sadly, changing market conditions along with a shortage of suitably-skilled labour forced a cessation of the company's model engine manufacturing activities in 2013.
Full details of the Aurora company's activities over the years may be found in a separate article on this website.