Well, after much online searching I found one rotospader manual. It's not the same model as mine, but it lookes nearly the same according to the pictures and parts lists.
Here is a link to the manual I found (.pdf): http://www.mediafire.com/view/?g6uaajjwvwadnnc
The guy I bought mine from said there were some seized pulleys and bearings would have to be replaced. I took it apart last night and there are not seized pulleys, the transmission feels smooth (turning by hand), and the only real problem seems to be that the belt was rusted in place on one of the pulleys, which is why I think he thought the pulley was seized. That was easy enough to remove. I already found an engine gasket kit, a replacement belt, and some other random parts so hopefully I can get this thing running soon!
Not sure how I did this, but after hours of searching online for manuals yesterday, I found another one online today with a single google search. This manual is for a similar rotospader model #785.292050 (1972, 5HP briggs and stratton, power reverse).
Also, the webpage containing this manual link has a bit of info about the rotospader, pics, a link to the engine user manual, and a link to an engine parts list for B&S engine model series 130900 to 130999. Here is the link: http://www.phoenixfab.net/RotoSpader/RotoSpader.htm