I don't have much information about the Willys Utility line of vehicles, but with those casting numbers I'd say that the engine is close to, but no later than 1949.
I'd say that engine serial number is from about 1949 or so. The casting number and other cast characters from the driver and passenger sides, down low, near the rear would help to date it. Check out the Norton Young Willys-Overland Production Figures over on the CJ-3B Page. https://cj3b.info/WOfigures.html This shows that Willys did use an "SW" designation.
These do exist as a real L134 prefix, but they don't seem to be very common. 4 usually means it was in a 4 wheel drive vehicle. SW...Station Wagon? That said, Willys seemed to use the "U" prefix in their Wagons. I don't think they called their wagons "Station Wagons" back then.
What is the engine casting number? It is found along the lower edge of the block down by the oil pan, on the passenger side. There are possibly some numbers on the driver side too. If so, what are they?
Bob Westerman may be able to help. He might see this post, but I recommend sending him a PM. He could have the answer.