If it has the original engine, you might be able to go to a site like this:

http://www.milacalawn.com/parts.asp

and determine the year of the engine.

Search Google for Sears Suburban and take a look at the tractors. Also look at searstractor.com

mike merritt

Here is a link that might be useful: searstractor.com

Have you contacted Sears parts department? With the model number they can usually provide a date of manufacture.