not sure of the exact years but if it has a round barrel it's a good one your safe with a red face unless someone swapped it out to an octagon. the picture below is of my 67 redface, on the lefthand side behind the idler is the barrel it is the part with the mounting bracket on the bottom going to the frame. My 81 has an octagon barrel but still welds good, the only thing about the ones with aluminum in them is that they start off the day like any sa 200 but then as they warm up you have to keep turning up your remote more to get the same heat.  then you stop for coffee and they cool off fast and you have to go through it all over again. most copper machines with be off by about 10 in the morning. You can smoke a rod to warm things up a bit but usually just blaze and adjust to it.

[IMG]http://i128.photobucket.com/albums/p185/downhandonly/sa2003.jpg[/IMG]