What kind of Briggs are you talking about?
If it's an old flathead, it really won't be picky about oil and will run happily on a straight thirty or forty, 10W-30, 15W-40, 15W-50 or whatever other odds and ends you have laying around the garage.
I just realized that I'm replying to a ten year old topic starter.
I still have all of the OPEs I had in 2003, and have not actually bought any since then.