Use part numbers to check for differences, also the part diagrams can help, but they are often fairly generic for several years. Only down side with part number is that they don't tell you what changed, just that there is a change. I normally check ebay listings to try to spot the difference.
1981 - https://www.partzilla.com/catalog/ho.../1981/atc200-a
1983 - https://www.partzilla.com/catalog/ho.../1983/atc200-a
Seems to me the 82 185S I had, was side mount exhaust. Not sure if I have that around yet or not or what kind of shape it's in.