Darren:
Take a look at the left rear corner (all directions as if you are sitting in the driver's seat)... the angle iron that held the upper rear vertical plate may still have the hull number stamped on it.
Look about one inch in from the left side. The stamoped numbers are about 1/3 inch high.
With the hull number you may be able to narrow the range of the carrier serial number which would help date it for you. there are a couple of registers out there that compare hull and serial numbers.
Good luck!
Mike