First models of the 62 came out in late 64 early 65. There was a second version which appeared in mid 65, they have a thinner style cab. The early version also have a slightly tilted baffle board (tilts up) and should have a pair of 20 watt Celestions in it. The amps also came stock set up for KT66 power tubes. The early models the original style script Marshall logo and what was referred to as a snakeskin grill (you might be able to find pics of this on the web). I also know these amps have more of the original Tweed tone stack in them with some slight changes in cap and resistor values.
If you scored an original for a grand you did really well. A good friend of mine has an original second version as well as a two year old reissue. Great sounding amps.
How about some pics?