dug an old bike out at my parents place

I was at my parents farm and my dad had mentioned he had an old motorcycle out in the back shed, so me and a friend went back and dug it out.  To my amazement it was a combat.  the engine is there, and bike is there, I will be restoring it with a friend, and he does car restorations and painting, etc... so he knows what to do and what not to do.  the id tag on the head of the frame shows 7/1973 (which the plastic part has the number 7 on it)  chome tank, and the serial number is D-24841.

I am looking for more information regarding this bike as I'm not sure what the 7/1973 is, I know 73 is year of production, and from the brief research I found the serial number means we have there was only 900 made.  


the bike was a bit rough, but looking at it, it's all there, so were going to restore it and post the before and after pictures on here as well as in my small town there is a car and bike show every october (pumpkinfest in port) which they never have dirt bikes.


so my question is what does the 7 mean and is this a rare one, only 900 made?

thanks in advance, and will post pictures soon.


thanks, and may be looking for help along the restore.