As the others have said, there is no other way to find out what the serial number was. The heat codes don't help much in the styled years. You likely can determine what year it is by the parts that are on it. Start with the big changes and narrow it down from there. Cast frame or angle iron frame? If cast, does it have pressurized cooling or not? A parts book is a huge help when trying to narrow down what you have.
Paul, a shout out to you and a big thanks for some wonderful stories in Green Magazine. In line with my always being interested in little details, historical and informational stuff about Deere, I have been purchasing and reading back issues of GM over the last couple years. I've been copying and filing little tidbits of info and stories, and have at least a couple of yours. Very good stories, you should write more. Maybe you do?
P.S. Also have read several good stories/articles from a much younger Jake Winn, FIT, and some others on here. Thanks to all of you.