OEM Manufacturers will often recommend a different weight than the engine manufacturer, simply for the fact that they might not sell the recommended oil weight. For instance, John Deere recommends their 10W30 conventional while Briggs recommends 5W30 synthetic as the best choice, followed by SAE30 as the second best choice. 10W30 conventional is their third recommendation, but they caution that the engine will consume oil above 80 degrees F.
If that were my engine, I would use the recommended 5W30 synthetic. It can handle the heat and does a good job keeping the engine/rings/valves clean of deposits.
FYI, that engine uses 1.5 quarts of oil, so go buy a 5 quart jug at Wal-Mart and have enough for top offs and oil changes for several seasons.