Whoa...a 320 is not in the same family as the 316, 318, 322, 330, 332, etc. It would seem so, but this model is when JD did the pardignm shift in the model series. So, it won't accept the attachments of those old 300's.
It looks like this...
A 320 is similar to the 240, 260, 285, etc. It would be the prerunner to the 325 and 345. It's a mid-level garden tractor.
It was a good tractor for sure though. 18hp Kawaski L/C twin and hydraulic lift. $1,500 would be top dollar, and it had better be a cream puff.