There were 47 or 48 pre-production prototypes ( as Blackadder said in another context, opinion is divided) all 80" galvanised steel chassis. The very first was centre steer, of the others there were both RHD or LHD.
25 were built before the official launch (Amsterdam Motor Show 1948) and the rest immediately afterwards. Of the two taken to Amsterdam for the launch one was RHD for display and one LHD for demonstration.
I think that any prototype with its original chassis and/or engine should have single or double digit chassis or engine numbers - for example Chassis no R32 Engine number 33 was one of two prootypes supplied in 1948 to the National Insititute of Agricultural Enginnering for long term testing.
Sanjay, why not try the Series One club - they should be able to give you chapter and verse if you can give them serial numbers as well as photos.
My gut feel is that you have a production series 1, but not a pilot-run model, that still puts it between 1948 and 1954 if its on an 80" chassis