To the best of my knowledge 9/84 is when deck height changed. I have been searching for a link to decode engine stamp with no luck so far. I am running into similar problems with rebuilding a block and figuring out what year it really was manufactured.
As far I have read the "laser block", is 9/84 and newer, is the "short" engine, which also doesn't have enough room for a double chain conversion. Maybe that will help you identify manufacturer date. If I am wrong, I stand corrected.
