I recently purchased a sad looking CS 3-1 from a swap meet. The first thing that caught my attention was the placement of the fuel filter, attached to the side of the head rather than the barrel and the importer/distributor plaque riveted to the side of the value cover. The fuel pipe from the filter to the pump was, of course, twice the normal length, with banjo connectors at both ends. Going by the Serial number CS 8989 it was built in 1933 which I'm told was the first year of production of the CS 3-1's. Is it possible that Lister experimented with the placement of the fuel filter in 1933? It also has a thick plan steel oil filler lid instead of those cast iron ones with the "K" on them. It also has a matched pair of flywheels with a different serial number, IE. CS 12243 from 1934

What I forgot to mention is that the fuel filter wasn't just put there by a previous owner. When I unbolted it from the head, it exposed two large circular water jacket holes, so the fuel filter was definitely meant to be there as the cast iron holding bracket forms part of the water jacket of the head assembly.   

I also have a 1940 CS 3-1 that looks normal so I know the difference

Cheers

Mark