another 2 cents worth, I have used both straight 30 and multi grade oils for about 20 years in antiques. Mostly motorcycles though, they rev fairly high and run hot. No problems at all, just keep your oil clean. The oils today are far better then what they had in the good ol days I've always been told, just keep it clean. I took a look at synthetic oil the other day, could not believe the price. I will stick with the cheap stuff, it has worked good for me. My 39 Indian has run about 50,000 miles on 30wt, I run 20 - 50 in my Henderson, straight 30 in my truck, good luck.
