Atcos of that era and later used their own fuel tank, hence no SIF tank fitted. The exhaust is out of period with the air filter which is definitely an early one. A matching exhaust would have been a one piece cylindrical one set at an approximately 30 degree angle pointing away from the carb. They were a bit of a pain as the carb had to be removed to allow them to be installed or removed. The later pattern on you machine consisted of a threaded pipe screwed into the block with an easily replaceable box secured by a single brass nut. The weak point of this later design was erosion and shearing of the threaded spigot for the nut by the hot exhaust gasses, particularly if the brass nut had been replaces by a steel one. On both designs removal of the pipe from the block could be a pain involving making an internal cut with a hacksaw blade and collapsing the pipe.
On a machine of that age with an unknown history there is always the possibility that the engine may not be the one it left the factory with, but other than the colour s basically “right” for the date of the machine!
