I'm sure the Ford gurus will correct me, but I don't know of any wide 5 15" wheels, except maybe for early VW. All 36-39 wide 5's are 16". If you run 40-48 drums and hubs they are 5x5.5 and there are 15" wheels that will fit that BP. But you're kinda stuck with wide 5's unless you change the drums and hubs.
I think if you want the super wide bolt pattern in a 15” wheel that isn’t super super rare your Going to have to go shopping at a dirt track racing supplier. after that as long as nothing is keeping it from seating correctly I don’t know why you couldn’t bolt them on?
I have 15" Lincoln wheels and 15" merc wheels. Both 5 on 5.5 both have been bolted to 40 Ford drums. Pictured is one of the Lincolns
I have six 14" slot mags in 5x5.5 pattern. I run one pair on the front of my '40 from time to time. Used to run them all the time. I did have to take a grinder to the sharp inner edge of the rim just a bit so they were not sitting on the drum at that point. I now have F100 brakes on the front and at 11" brakes it is no longer an issue at all. Dave
So you don’t have stock 39 drums ( which would be wide 5), you have 40-48 drums and hubs. 15” wheels are no problem.