Yes, it is possible as they would have sold off the pre-production cars after main stream production was in full swing. The only snag with that is that they usually gave experimental/pre-production models a vastly different chassis/ID number - or at the very least, there may be some evidence on the car of the number having been changed into a more recognisable chassis number.
As POMMReg says - confirm whether the chassis plate number agrees with the number stamped into the bulkhead near to the wiring loom. If the two numbers are different, it would suggest that you have a chassis plate from an earlier car on your clearly later vehicle. If/when you find this, and if it is different to the plate, use the bulkhead number with Heritage folks to get the true identity of the car.
If the two are the same, then there is clearly something a bit different about this car. Aside from the location of the speedo, it is perfectly possible to make a later car look externally like an older car, and vice versa but the speedo location is the giveaway in both cases. Yours says post October 54 but if the info you have is correct, then you may well have some sort of pre-production vehicle. Good luck with the investigations and do keep us posted
