Check http://www.winbond.com.tw/ (taiwan)
I see various permutations of the 83C787 digits (e.g 83C877), but I do not see that part. Are you sure that your part is 83C787? You can download Winbond datasheets from that web site.. Is C787 an old ('486 days) part? My recommondation is to focus on recent chipsets first because data is more easily available and the results are most useful.
-Ray