more locomotives had been fitted with this system by the time TOPS renumbering occurred (some of which retained the steam heat facility following ETH fitment whilst others had it removed at that time), and shortly afterwards the sub-class had settled down to 154 locomotives, numbered 47401–47547 and 47549–47555. Later, further Class 47/0s were converted to Class 47/4s and renumbered into the series from 47556 onwards, which eventually reached 47665. Class 47/6 and Class 47/9 After being severely damaged in a derailment near Peterborough in 1974, locomotive 47046 was selected to be a testbed for the projected Class 56, and was fitted with a 16-cylinder Ruston 16RK3CT engine rated at for assessment purposes. To identify it as unique, it was renumbered 47601 (at the time the number range for Class 47s only extended as far as 47555). Later, in 1979, it was used again for the Class 58 project, fitted with a 12-cylinder Ruston engine (this time of ), and renumbered 47901. It continued with this non-standard engine fitted until its withdrawal in 1990. Class 47/7 In the late 1970s, BR authorities identified a need to replace the ageing trains operating the Glasgow to Edinburgh shuttle services, in order to increase speed and reliability. The trains were operated by pairs of Class 27s, one at each end of this train. It was decided to convert twelve 47/4s to operate the service in push-pull mode. The locomotives would be known as Class 47/7 and would be fitted with TDM push-pull equipment and long-range fuel tanks, and be maintained to operate at . The conversions began in 1979 and the service was operated completely by them from 1980. In 1985, the push-pull service spread to Glasgow-Aberdeen services, and a further four locomotives were converted. The sub-class therefore comprised 47701 to 47716, though a further locomotive, 47717, was converted in 1988 after the fire-damaged 47713 was withdrawn. Class 47/7b and 47/7c In the 1990s, further 47/4s were converted with long-range fuel tanks and equipment to allow them to work with a type of rolling stock known as propelling control vehicles-PCV, which utilised RCH (Railway Clearing House) cables to allow the PCV driver to signal to the driver on the locomotive to apply power and operate the brakes - neither these locomotives or the PCVs were equipped with TDM push-pull equipment. They were also numbered into the 47/7 series, from 47721 onwards. With dwindling passenger